Manual Release checklist

We now do this automatically in CI.

Revise CHANGES.md, plugin-gradle/CHANGES.md, and plugin-maven/CHANGES.md
If necessary, release lib ./gradlew :changelogPush
Release the plugins one at a time ./gradlew :plugin-XXX:changelogPush
Test latest spotless on:
- Gradle via Apache beam at v2.13.0: https://github.com/apache/beam
  - bump the spotless version in buildSrc/build.gradle
  - ./gradlew spotlessApply -PdisableSpotlessCheck=true
- Maven via JUNG at bf7e5b9: https://github.com/jrtom/jung
  - bump the spotless version in pom.xml
  - mvn spotless:apply -U
  - might take a while for mavencentral to update, the -U flag above ensures that it tries again rather than caching a failure
Comment on all released PRs / issues