feat: PAT for PR creation + better release changelog

[tchataigner]

This PR changes the PR creation flow to use a PAT, this will alow us to trigger CI on automated PRs. It also changes the way we generate changelog for releases:

• On release: Look for latest major or minor release for the given light client and compile changes since then.
• On new Light Client release: Compile the changes solely on the folder that is allocated to this light client
• On hotfix: Compiles the changes since the latest patch of the version