[skia auto roller + cocoon] request handler to process release branches

[XilaiZhang]

context: https://github.com/flutter/flutter/issues/109255.

This PR fetches latest stable, beta and google 3 branches based version numbers. e.g. For stable branch, it is assumed that a branch tagged with 3.0.4 will be newer than a branch tagged 3.0.3. For google 3 branch, it is assumed that flutter-1.23-candidate.10 will be newer than flutter-1.23-candidate.9.