Add Rocket.Chat migration guide

[vish9812]

Summary

Depends on PR - mattermost/mmetl#96

Adds documentation for migrating from Rocket.Chat to Mattermost.

• New guide: onboard/migrate-from-rocketchat.rst — documents the Rocket.Chat → Mattermost migration path using mongodump and the mmetl transform/check commands, including guest users support.
• Links the new guide from the migration index (manage/admin/migration.rst) and the server migration overview (onboard/migrating-to-mattermost.rst).

[vish9812]

⚠️ Do not merge until the mmetl Rocket.Chat migration PR is merged first: mattermost/mmetl#96

This guide documents the mmetl transform/check commands for Rocket.Chat, which depend on that PR.

[Copilot]

Pull request overview

Adds a new Rocket.Chat → Mattermost migration guide to the admin docs, and wires it into the existing migration navigation so admins can discover and follow the new path alongside other platform migrations.

Changes:

• Adds a new migrate-from-rocketchat.rst guide covering export (mongodump), transform/check (mmetl), and import (mmctl).
• Links the new Rocket.Chat guide from the server migration overview page.
• Adds the new Rocket.Chat guide to the migration index/toctree.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 4 comments.

File	Description
source/administration-guide/onboard/migrating-to-mattermost.rst	Adds a “Move from Rocket.Chat” section that links to the new guide.
source/administration-guide/onboard/migrate-from-rocketchat.rst	New end-to-end migration guide content (prep → export → transform → import → validation).
source/administration-guide/manage/admin/migration.rst	Adds the Rocket.Chat guide to the migration index/toctree and bullet list.

[github-actions]

Newest code from mattermost has been published to preview environment for Git SHA 28a4c55

[github-actions]

Newest code from mattermost has been published to preview environment for Git SHA 28a4c55

[coderabbitai]

📝 Walkthrough

Walkthrough

This PR adds a new documentation page describing how to migrate from Rocket.Chat to self-hosted Mattermost, covering preparation, export, transform, import, post-import remediation, migration coverage, and FAQs. Links to this new page are added from the migration index and migrating-to-mattermost overview pages.

Changes

Rocket.Chat migration documentation

Layer / File(s)	Summary
Navigation links to new guide `source/administration-guide/manage/admin/migration.rst`, `source/administration-guide/onboard/migrating-to-mattermost.rst`	Adds toctree and bullet-list entries linking to the new Rocket.Chat migration guide from existing migration documentation pages.
Guide intro and preparations `source/administration-guide/onboard/migrate-from-rocketchat.rst`	Adds the document title, overview of the export/transform/import approach, and a preparations section covering scope, prerequisites, storage considerations, and Mattermost configuration changes.
Export and transform steps `source/administration-guide/onboard/migrate-from-rocketchat.rst`	Documents the `mongodump` export step and the `mmetl check`/`mmetl transform` steps, including flags, expected output, and failure handling.
Import and post-import remediation `source/administration-guide/onboard/migrate-from-rocketchat.rst`	Documents `mmctl import` steps including the large-import file store method, post-import SQL fixes for unread state, and placeholder email/account activation behaviour.
Migration coverage reference and FAQ `source/administration-guide/onboard/migrate-from-rocketchat.rst`	Adds a "what migrates and what doesn't" table, custom emoji handling notes, and an FAQ covering common questions and troubleshooting.

Estimated code review effort: 2 (Simple) | ~15 minutes

Related issues: None specified in the provided context.

Related PRs: None specified in the provided context.

Suggested labels: documentation

Suggested reviewers: None specified in the provided context.

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🐰 A hop from Rocket.Chat, a leap to a new home,
mmetl and mmctl guide the way we roam,
dumps and transforms, a careful migration dance,
docs now lit with every configured chance,
a carrot for the guide, no longer left to chance.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely matches the main change: adding a Rocket.Chat migration guide.
Description check	✅ Passed	The description accurately summarizes the new guide and the added navigation links.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch add-rocketchat-migration-guide

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_{Comment @coderabbitai help to get the list of available commands.}

[coderabbitai]

Actionable comments posted: 2

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@source/administration-guide/onboard/migrate-from-rocketchat.rst`:
- Around line 69-74: The migration prerequisites in the onboarding guide are too
broad and should be framed as temporary changes. Update the guidance around the
configuration settings list in migrate-from-rocketchat.rst, specifically the
entries for TeamSettings and EmailSettings, to say they are only needed during
the import and must be reverted immediately after. Make it clear that
TeamSettings.MaxChannelsPerTeam, TeamSettings.MaxUsersPerTeam,
EmailSettings.EnableSignUpWithEmail, and EmailSettings.EnableSignInWithEmail are
migration-only adjustments rather than permanent configuration changes.
- Around line 197-226: The post-import SQL in the migration guide is too broad
because the `preferences` updates for `direct_channel_show` and
`group_channel_show` affect every user, not just the imported cohort. Update the
instructions around the `preferences` statements in the migration snippet to
either scope those changes to the imported users only or remove them if they are
not required, using the same `channelmembers`/`preferences` flow shown in the
guide; if the global change is intentional, explicitly document that side effect
in the surrounding text.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Pro

Run ID: badcd8dd-0ba4-4a55-acef-e8c8ede9fabb

📥 Commits

Reviewing files that changed from the base of the PR and between 3c001a7 and 28a4c55.

📒 Files selected for processing (3)

• source/administration-guide/manage/admin/migration.rst
• source/administration-guide/onboard/migrate-from-rocketchat.rst
• source/administration-guide/onboard/migrating-to-mattermost.rst

[github-actions]

Newest code from mattermost has been published to preview environment for Git SHA f617cfb