[WIP] autopublish version-bump pushes

[MattSturgeon]

High level concept: when main is pushed to, check whether it's current version has a release associated with it. If not, publish one.

• For simplicity, this is integrated into the existing build.yaml workflow.
• During the prepare job, if the event is a push to main, we check if a github release is published for the current version.
• The actual build runs in a matrix and uploads workflow artifacts.
• Additionally, the matrix concurrently builds :publish.
  • :publish builds a jar from kotlin sources and generated release-publishing metadata.
  • The JAR will be responsible for publishing, if the current version is unreleased.
  • :generateReleaseMetadata is a rootProject task that outputs release metadata, such as the changelog.
  • Additionally, it aggregates loader-projects' :generateReleaseMetadata tasks. These represent version-specific info, like "dependency relationships", MC version, supported loader.
  • The rootProject task collects the loader-project' outputs and embeds it within its own output as the versions array.
• After the build, if prepare determined a release is needed, a publish job downloads all workflow artifacts and publishes them.
  • The :publish tarball is also downloaded as an artifact, but not itself published.
  • Instead, it is extracted and installed onto the CI workflow's PATH.
  • It then reads its embedded metadata json and publishes artifacts to GitHub, Curseforge, & Modrinth (or does a dry-run for PRs).
  • WIP

The release workflow will be:

1. Decide we need a release
2. Bump the version in gradle.properties
   • Optionally, using :bumpVersion
3. Patch the changelog using :patchChangelog
4. Make a commit
5. Make a PR
6. CI validates changelog corresponds to version
7. Merge PR
8. CI builds & releases automatically
9. If publishing failed, CI will try again next push, because "main branch version is newer version than latest release" will be unchanged.

TODO:

• Drop modpublisher
• GitHub workflow
• Generate release metadata
• Base publisher
• GitHub publisher impl (mostly done)
• Modrinth publisher impl
• Curseforge publisher impl