add coverage reporting

[sroet]

This should add coverage and coverage reporting as a github action

[sroet]

hmm this can't easily be done with github workflows, without external parties due to github security. (It does not allow any workflows that run on a PR from forks on public repos to have write access to anything, which is required to write a comment on the PR with the required info).

There is technically an example roundabout way of dealing with it: https://github.com/py-cov-action/python-coverage-comment-action which I could look into.

Otherwise, I can probably set it up with an external party:

• codecov.io (an example PR, click on "view details" on the merge commit to see the actions/checks on top of the comment)
• coveralls.io (example PR, does not comment, but does give a check)
• codacy (I don't think I ever set up this one, but do know it exist. example PR)
• Any other?

@McHaillet which of the following would you prefer? (I slightly prefer to see if I can get the roundabout way to work)

[sroet]

Hmm, I just realized that the codecov reporting code will probably not work as it pulls some data to figure out which PR to post stuff to, which is then run on a pipline that has no reference to that PR...

[sroet]

alright, switched to another package that should work
@McHaillet please have a look (it will not work properly before coverage.yml is actually in the repo)