Validation of test_cases and test_levels

[mattias-p]

Depends on:

• Test module registration #1335

Today the documentation of the test_cases and test_levels profile properties prescribe sets of valid property values, but the no corresponding validation is performed. The Profile module should be updated to validate the contents of these properties.

Before implementing this the Profile module should have knowledge about the names of all available test cases. The Profile module should not depend on the Zonemaster::Engine::Test module, the required information will be available to the Profile module after #1335.