Track PR release version with labels/milestones

> Somewhat related to this, I think it would be nice if a merged PR had a way to quickly tell which version it applies to (or will apply). Sometimes in the past I had to check the changelog to confirm if a PR got in the current release or not. We could use milestones (like Rust or Kubernetes), or regular labels (like Helm):
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> This should be easy to do with actions that run on merge.
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> If then DataFusion supports an LTS version, we could add a label there as well so it is easy to tell that it was backported.

_Originally posted by @nuno-faria in [#16622](https://github.com/apache/datafusion/issues/16622#issuecomment-5648012129)_

cc: @alamb