Suggest label closed pull request with first release it's available in.

This is a suggestion to improve the release automation to make it very obvious when a given accepted pull request will be available by using labels to mark said pull requests. Specifically, it's a suggestion to do the following:

1. Add a new label for release candidate, e.g., `in-candidate-0.8rc00`
1. Apply said label to all closed pull requests that don't already have a relevant label that are in the release candidate.
1. When the release is finalized, add a label for the release, e.g., `in-release-0.8`
1. Replace the label of all `in-candidate-0.8*` with `in-release-0.8`
1. Clean up dead `in-candidate-0.8*` labels.

This could similarly be applied to issues fixed by commits in the release.

Some additional maintenance might be required, e.g., if a release is abandoned, may have to remove `in-candidate-` labels, or if a commit is later rolled-back, not sure how to have the system know not to apply that label.

No files, tests, or entry points are named. Start by locating the repository’s release automation and its GitHub label handling, then clarify behavior for candidate, finalized, abandoned, and rolled-back releases. Done means pull requests and related issues receive candidate or release labels consistently, with obsolete candidate labels removed.

Written by the indexing model from the issue text.