ci: enforce changelog

[miparnisari]

Description

This PR introduces a change in the release process.

Problems:

• make the release notes easier to write
• we don't have a useful changelog

Assumptions

1. the most important audience for the release notes should be (a) the users of SpiceDB and (b) SpiceDB's Product Managers (who write https://authzed.com/changelog). (*)
2. we want to follow https://keepachangelog.com/en/1.1.0/. which states

   • A changelog is a file which contains a curated, chronologically ordered list of notable changes for each version of a project.
   • Using commit log diffs as changelogs is a bad idea: they're full of noise

(*) this does not mean that there aren't other audiences. There are: SpiceDB developers. But, they can rely on commit history.

Proposal

Before

Now

On every relase, the release maker goes through the list of commits, picking what is important and writing summaries of each change (perhaps requesting help from PR authors to write said summaries). The release maker has liberty of including whatever they like.

On every PR, the PR author MAY add an entry in the CHANGELOG.md. The maintainers review it and request amendments or approve it. The PR author MAY decide not to include the change in CHANGELOG via a label skip-changelog, but generally every commit with prefixes fix, feat, perf should be included. On every release, the release maker copies the changelog entries for this release and pastes them in the release notes.

Testing

$ npx keep-a-changelog
Updated file /Users/miparnisari/Documents/GitHub/spicedb/CHANGELOG.md

[tstirrat15]

LGTM

[tstirrat15]

Still curious to see what this looks like in practice - I'm a little worried that it's effectively going to duplicate the release content - but I'm okay with learning that when we do the next release.

[miparnisari]

[tstirrat15]

LGGTM

[tstirrat15]

LGTM