feat: update releases when release branches change

[Nostracodus]

This change enables automatic PDF generation for releases when release branches are changed. This supports backporting changes to prior releases.

This works by:

• Creating a branch named release/XYZ, where XYZ is the name of a release, when a release is made.
• Activating PDF generation when release/XYZ branches are changed.
• Updating the release XYZ when PDF generation is finished.

The release may be named anything. The only portion of the name that is important for these actions is release/ in the branch name.

The generated PDFs will be accessible from the Release pages and the links to these PDFs are stable.

No manual work needs to be done beyond creating a release. All other steps should happen automatically as normal development happens.