[DOCS] Add examples and authorization details for changelog upload

[lcawl]

Relates to #3470

This PR augments https://docs-v3-preview.elastic.dev/elastic/docs-builder/tree/main/cli/changelog/upload

AI summary

Created docs/cli/changelog/cmd-upload.md which contains:

• Description of the command and incremental upload behavior
• Artifact types table (bundle vs changelog) with default directories
• Upload targets (s3 vs elasticsearch)
• S3 bucket structure — object keys and registry.json manifest paths
• Configuration — --directory, --config, and resolution order
• Four examples matching the style of cmd-bundle-amend.md

Generative AI disclosure

1. Did you use a generative AI (GenAI) tool to assist in creating this contribution?

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• No

2. If you answered "Yes" to the previous question, please specify the tool(s) and model(s) used (e.g., Google Gemini, OpenAI ChatGPT-4, etc.).

Tool(s) and model(s) used: composer-2.5-fast,

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• docs/cli/changelog/cmd-upload.md

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📝 Walkthrough

Walkthrough

A new documentation file (docs/cli/changelog/cmd-upload.md) is added, covering the docs-builder changelog upload CLI command. The page describes local artifact discovery (YAML/Bundle), required and optional flags (e.g., --s3-bucket-name), S3 upload behavior with content-hash incremental support, registry refresh semantics, the unimplemented --target elasticsearch path, S3 object key structure, configuration and directory resolution order, and multiple usage examples.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title directly reflects the main change: adding documentation examples and authorization details for the changelog upload command.
Description check	✅ Passed	The description is clearly related to the changeset, detailing the new documentation file, its sections, and the purpose of the PR.
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.

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✨ Finishing Touches

✨ Simplify code

• Create PR with simplified code
• Commit simplified code in branch changelog-upload-examples

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[Mpdreamz]

Not important but we will never implement this like this,

We will do a background job syncing S3 to Elasticsearch.

[lcawl]

Yeah, that makes more sense. I've left as-is for now since that's apparently how it currently functions.