Integrate Sonar Cloud for test coverage reporting

[monocongo]

Is your feature request related to a problem? Please describe.
We've decided to try using SonarCloud for test coverage reporting.

Describe the solution you'd like
Integrate the SonarCloud test coverage reporting into our GitHub Action workflow for unit tests.

Describe alternatives you've considered
We've used coveralls in the past, but the UI is clunky and hard to navigate, now giving Sonar a whirl.