Setup release plan

[NullVoxPopuli]

What's release-plan?

A hybrid of the best parts of release-it and changesets.

Repo / docs here: https://github.com/embroider-build/release-plan

This allows folks with GH Maintainer access to preview and release to npm without actually needing to have any keys locally on their machine (or access to the npm package, which makes management of the repo separate from the npm package easy and encouraged).

• Everything is automated via GH Action workflows.
• We release by merging the "prepare release" preview PR.
• Changelog entries are determined by labels on the PRs (see release-plan readme)
  • we edit the changelog text via editing the PR title

See the newly added RELEASE.md for details.

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Why release-plan?

• release-it doesn't work with pnpm-workspaces there is this, but it's been too long
  • no need to do this every release: https://github.com/ember-cli/ember-page-title/pull/279
• release-plan is maintained by the tooling team.
• anyone with maintainer access on GH can do a release
  • no need for local tokens (good security)
  • no need to have maintainers have push-to-main/master access (good for repo health)

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Growing list of users: https://github.com/embroider-build/release-plan/network/dependents