PR template

[housa]

To help contributors, as well as maintainers of the repo, we should have a PR template containing all the important steps we want to make sure have been handled for a PR to be ready for review, this will then also serve as a list for the maintainers, when doing the review.

[housa]

Make sure to also add relevant info in the contributing.md

[housa]

https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/creating-a-pull-request-template-for-your-repository