Create workflow for detecting charm lib out-of-date, and propose a PR

Charm lib can be out-of-date when there is a new release, manually checking and updating lib is time consuming. We should automate this process in a workflow.

The issue does not name a file, test, or existing workflow. Start by inspecting the repository's charm-library layout and current automation, then determine how library releases are identified. Done means an automated workflow detects an outdated charm library and proposes a pull request.

Written by the indexing model from the issue text.