Publish snapshots

[jackkoenig]

Remove custom publishing logic, use upstream flow instead.

This involves generating the list of plugin versions we publish. Once we start publishing Scala 3 versions we can remove this logic.

I tried doing this programmatically in Mill code, if you look at the individual commits you can see how unwieldy this got and I'm not super keen on maintaining that code. I think this approach is the least bad option.

Draft PR for now so I can test the Github Actions flow.

Contributor Checklist

• Did you add Scaladoc to every public function/method?
• Did you add at least one test demonstrating the PR?
• Did you delete any extraneous printlns/debugging code?
• Did you specify the type of improvement?
• Did you add appropriate documentation in docs/src?
• Did you request a desired merge strategy?
• Did you add text to be included in the Release Notes for this change?

Type of Improvement

• Internal or build-related (includes code refactoring/cleanup)

Desired Merge Strategy

• Squash

Release Notes

Users can access these SNAPSHOTs using the Maven Central Snapshots repository: https://central.sonatype.com/repository/maven-snapshots/

Reviewer Checklist (only modified by reviewer)

• Did you add the appropriate labels? (Select the most appropriate one based on the "Type of Improvement")
• Did you mark the proper milestone (Bug fix: 3.6.x, 5.x, or 6.x depending on impact, API modification or big change: 7.0)?
• Did you review?
• Did you check whether all relevant Contributor checkboxes have been checked?
• Did you do one of the following when ready to merge:
  • Squash: You/ the contributor Enable auto-merge (squash) and clean up the commit message.
  • Merge: Ensure that contributor has cleaned up their commit history, then merge with Create a merge commit.

[seldridge]

LGTM

[jackkoenig]

I don't think this is actually working yet. As far as I can tell it publishes the SNAPSHOTs but its sending them to the wrong URL where they are then rejected: