ci: replace auto canary releases with pkg.pr.new

[jackw]

What this PR does / why we need it:

This is the first of three PRs which will remove Auto from the repo and the need for bypassing gh branch rulesets.

Replaces Auto's PR-time canary publishing with pkg.pr.new, and gates the existing release job to push-to-main only.

• Adds .github/workflows/preview.yml that publishes affected packages to pkg.pr.new when a PR has the preview label. The pkg-pr-new[bot] will post a comment with installable SHA-keyed URL instructions.
• Gates ci.yml's release job with event_name == 'push' && ref == 'refs/heads/main', so auto shipit no longer fires on PR events. Auto's main-branch publishing is untouched and continues until PR 2 lands.
• Adds a Preview Your Changes Before Release section to the root CONTRIBUTING.md and trims packages/plugin-e2e/CONTRIBUTING.md to point to it.

Which issue(s) this PR fixes:

related: #2685
related: https://github.com/grafana/grafana-catalog-team/issues/943

Special notes for your reviewer:

[github-actions]

Hello! 👋 This repository uses Auto for releasing packages using PR labels.

❌ This PR cannot be merged until the following issues are addressed:

• This PR is missing one of the following labels: patch, minor, major, no-changelog.
• Optionally if using a patch, minor or major label also add the release label if you would like this PR to trigger npm package publishing.

🏷️ More info about which labels to use

• If the changes only affect the docs website, documentation, or this repository's tooling add the no-changelog label.
• If there are changes to any of the npm packages src files please choose from one of the following labels:
  • 🐛 if this PR fixes a bug add the patch label
  • 🚀 if this PR includes an enhancement add the minor label
  • 💥 if this PR includes a breaking change add the major label
• Optionally, if you would like this PR to publish new versions of packages when it is merged add the release label.

[Copilot]

Pull request overview

This PR updates the repository’s CI/release process by replacing PR-time canary publishing (via Auto) with label-gated preview publishing through pkg.pr.new, and by ensuring the existing release job only runs on pushes to main.

Changes:

• Added a new preview workflow that publishes workspace packages to pkg.pr.new when a PR is labeled preview.
• Gated the ci.yml release job to run only on push events to refs/heads/main (preventing PR-triggered releases).
• Updated contributing docs to describe the new preview flow and to point package-specific docs to the root instructions.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
packages/plugin-e2e/CONTRIBUTING.md	Replaces Auto canary instructions with pkg.pr.new preview-label workflow guidance.
CONTRIBUTING.md	Adds a new “Preview Your Changes Before Release” section documenting pkg.pr.new usage.
.github/workflows/preview.yml	Introduces a new PR-labeled preview publishing workflow using pkg-pr-new.
.github/workflows/ci.yml	Restricts the release job to pushes on main only.

[xnyo]

LGTM!

[pkg-pr-new]

Open in StackBlitz

@grafana/create-plugin

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/create-plugin@013d17e -D

@grafana/eslint-plugin-plugins

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/eslint-plugin-plugins@013d17e -D

@grafana/plugin-docs-cli

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/plugin-docs-cli@013d17e -D

@grafana/plugin-docs-parser

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/plugin-docs-parser@013d17e -D

@grafana/plugin-e2e

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/plugin-e2e@013d17e -D

@grafana/plugin-meta-extractor

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/plugin-meta-extractor@013d17e -D

@grafana/plugin-types-bundler

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/plugin-types-bundler@013d17e -D

@grafana/react-detect

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/react-detect@013d17e -D

@grafana/sign-plugin

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/sign-plugin@013d17e -D

@grafana/tsconfig

npm i https://pkg.pr.new/grafana/plugin-tools/@grafana/tsconfig@013d17e -D

commit: 013d17e

[sunker]

Very nice 👏

[ashharrison90]

lgtm 👍