This change introduces the builder pattern to the Marathon unit tests in
order to simplify and reduce the amount of testing boilerplate.
Additional changes:
- Add missing unit tests.
- Make all tests look consistent.
- Use dedicated type for task states for increased type safety.
- Remove obsoleted getApplication function.
Previously, we did the check too late resulting in the traefik.port
label not being effective.
The change comes with additional refactorings in production and tests.
