Figure out a plan to update release branches automatically

Release branches in client-python are following a release branch in kubernetes main repo. If there is a patch for main repo's branch, we should figure out a way to at least detect it, even better create a PR automatically and even much better merge that PR if it is backward compatible.

I would consider this task done if we create a PR automatically. Merging on backward compatibility would be just a plus.

Map how release branches in client-python correspond to the release branch in the Kubernetes main repository. Define how patches are detected and how an automatic PR would be created; treat automatic PR creation as done, with backward-compatible merging as optional.

Written by the indexing model from the issue text.