#2190 Add a default PR (and issue) template

[shokiami]

Resolves #2190

This PR should add a default PR and issue template. @misaugstad I am not exactly sure how to test if this works.

[shokiami]

@misaugstad Here is the documentation I used.

Creating a PR template:
https://docs.github.com/en/enterprise/2.14/user/articles/creating-a-pull-request-template-for-your-repository

Creating an issue template:
https://docs.github.com/en/enterprise/2.13/user/articles/manually-creating-a-single-issue-template-for-your-repository

[misaugstad]

Okay, I filled in the templates with a first draft. Fingers crossed that it works when I merge into master later!