Repo Management: maintain clean git history, utilize fast forward merge strategies

[emansom]

Description

Currently the merge handling is handled by GitHub itself, this has some drawbacks:

• Rewrites git history with useless pointers all over the place
  See https://blog.esciencecenter.nl/fast-forward-merges-on-github-752f900f45e8
• Creates useless Merge pull request X from Y commits when git histories diverge/do not align between source and target

Proposed solution

Adopt fast forward merge strategies described in the link above and here:
https://github.com/orgs/community/discussions/4618
https://stackoverflow.com/questions/60597400/how-to-do-a-fast-forward-merge-on-github

This can be accomplished semi automated by e.g. utilizing the following workflow:
https://github.com/marketplace/actions/fast-forward-merge

There is a potential supply chain risk there. Better to copy their code to our own GitHub workflows:
https://github.com/sequoia-pgp/fast-forward/tree/main/.github/workflows
https://github.com/sequoia-pgp/fast-forward/tree/main/src

[eduncan911]

I typically just set these on repos to enforce clean git history (the PR Title becomes the main's commit title).