Add support for test coverage

[EnricoMi]

Add simple reporting feature for test coverage.

[ksidirop-laerdal]

This feature becomes even more important considering that the alternatives in the github-action marketplace seem to be between non-existant, unmaintainable and/or unsuitable considering that they support only linux but not macos/windows.

[EnricoMi]

Looks like there are many different file formats to consider: https://docs.codecov.com/docs/supported-report-formats

[ksidirop-laerdal]

Looks like there are many different file formats to consider: https://docs.codecov.com/docs/supported-report-formats

You're probably already aware of this but just in case you're looking around for resources to gain inspiration from (and considering that most people use the now abandoned 'irongut/CodeCoverageSummary') here is the repo that show-cases how it's processing the cobertura format:

https://github.com/irongut/CodeCoverageSummary

Hope this helps a bit. Appreciate you running point on all of these things.