Agree and document contribution guidelines & PR process

[planetf1]

We need to clearly articulate the roles/responsibilities of parties involved in the code submission process, and how that process is executed. Ideally having some consistency within pq-code-package would be desirable

This should likely be places on our code documentation site (when agreed) and linked to from CONTRIBUTING.md in each repo

Specifically commit (merge / squash / rebase) should be considered. projects vary in their preference. I've tended to use merge, despite the noise (it seems much of k8s does too?) despite the merge commit noise

Lots of other areas to cover - getting started, code submission guidelines, local build/test, creating a good pr, release notes/docs impacts, templates, ci/cd checks, approval process/assignment .....