Add some issue/PR templates

[bollwyvl]

We should probably add some PR and issue templates.

For PRs:

• basically a checklist of:
  • did you open an issue first if it's a big change?
  • does this fix an issue?
  • did you target the dev branch Start a dev branch #154?
  • did you lint/build?
  • did you update the changelog?
  • did you add docs/example?
    • did you test?

For bug reports:

• we pretty much need to know the exact YAML someone is (at least) calling the action with, otherwise it's really hard to help
• at least the OS they are running
  • if it's a private (or on a self-hosted runner), they probably need a public demonstrator, or at least redacted logs of the output

For feature requests:

• whether it's just a feature demand, or whether they are going to PR
• how it can be tested

For documentation requests:

• some kind of guidelines, and some brown m&m's that they read the existing docs