Release process

I've reverted some usage of jreleaser to actually cut the release and got back to a simple script which triggers the workflow after having updated everything locally (it seems the ASF will not allow us to use GitHub actions which will commit/tag automatically).

So this is the first phase of our release process, which is mostly about generating the source distribution (the official _thing_ that is being released from an ASF pov) and the convenience binaries. The output will be something like https://github.com/apache/maven-mvnd/releases/tag/0.8.0

Now, once the vote on the ASF mailing list passes, we need to continue the release process and proceeded to
* generate checksums and signatures for the artifacts
* publish the artifacts (with signatures and checksums) on the ASF infrastructure (which has to be committed to the svn https://dist.apache.org/repos/dist/dev/maven repository)
* update the packagers: sdkman, homebrew, choco

@aalmiray given we can't really use actions, is there anything jreleaser can help us with ? I guess I'll have to use a script that the release manager will have to run anyway, because signing the releases involves using its private key which can't be done on the GitHub hardware

Review the simple release script and the GitHub Actions workflow that generate the source distribution and convenience binaries. Trace the post-vote steps—checksums and signatures, ASF SVN publication, and sdkman, Homebrew, and choco updates—and define a complete release run that covers them without automatic commits or tags.

Written by the indexing model from the issue text.