Fail check when coverage thresholds not met

[Weetbix]

Add the functionality to fail the action or a status check based on some metric coverage metric. This metric should be configurable through the actions parameters.

Some thought is needed on:

• Which metrics would be valuable to check for example:
  • Total coverage of the project
  • Total coverage of the new code
  • Delta coverage of the new code
• How best to fail. We can add a failed status check to the PR, or we can fail the Github action itself. We identify any advantages of each and choose which way to go