Implement workflow for a monorepo with fixed versions

This tool should be able to support a monorepo package that uses a fixed versioning scheme (e.g. `snaps-skunkworks` and `eslint-config`) in the same way that `action-create-release-pr` does.

Start by reading the repository entry points and comparing the requested workflow with the referenced action-create-release-pr behavior. Trace how monorepo packages and versions are currently handled, then verify the workflow using examples such as snaps-skunkworks and eslint-config. Done means fixed-version packages are supported consistently when creating release branches.

Written by the indexing model from the issue text.