Experiment with PR templates

[coyotesqrl]

Description

We are currently working on a multi-issue experiment #4289 to improve workflow and transparency. It's reasonable to assume we could get similar process improvements by incorporating multiple PR templates as well.

I'm not quite sure what/how many is appropriate for PRs and would like to see some conversation on the topic. Off the top of my head, I think templates for

• Bug fix (dependency upgrades would fit in here as well, I think?)
• Documentation
• Improvement (and/or new feature)
• Repository meta

would work well. These are granular enough that we could include different body elements, tags, and even assignees in the case of Docs and Repo meta where there are committers who actively work those very specific areas long term. They are not so granular, I think, that we're making noise for no value.