Add code coverage GitHub Action

[aloisklink]

It seems like the CMake/CodeCoverage.cmake file wasn't being used, so I quickly added a GitHub Action for it.

Currently, the coverage action runs after all tests pass, since it only makes sense to check coverage if tests pass. I've also kept it as a separate cmake action, as it requires lcov, which is not normally installed by people.

[github-actions]

LCOV of commit d717307 during Build #853

Summary coverage rate:
  lines......: 43.7% (5762 of 13186 lines)
  functions..: 59.7% (549 of 919 functions)
  branches...: no data found

Files changed coverage rate: n/a

[mereacre]

Great ideas.