Policies around Issues / PRs

[sbfnk]

I have a few questions around Issues / PRs that I don't think have been discussed yet (except partially with @Bisaloo in private):

• do we want to enforce/recommend proposing new features or fixes as Issues or Discussion items (and thus opening them for comments) before submitting a Pull Request?
• do we want to (self-)assign Issues before work starts on them to avoid duplication of effort? Would the person submitting an Issue usually be expected to be the person to address it?
• do we want ideas for new features as Issues or in the Discussion board?
• who merges PRs? The person to open it or a group of maintainer(s) of the package? If maintainer(s) I think we should encourage the use of Draft PRs to show work in progress and avoid premature merging.

Once clarified these could be added to the contribution guide being edited in this PR.