[RFC] Improve PR/CI <> `git log` workflow

### description

there have been some questions around the CI <> git log workflow, and how we might automate this

this is a tracking ticket to get some ideas on how this could be achieved

ideally suggestions should address

- what information should be stored in the `git log` and why
- my own feeling is that parsimony is valuable here
- for PRs
- what information should be stored on a PR
- how the information should be structured
- who can add any salient information
- automation/triggers according to eg tags or comments