What/Why:
Currently maybeValidateInternal() skips certain validators via a hardcoded skip list (Z6184, and Z831 (until it's removed in T418886)). This is fragile and future validators in the same situation would need to be manually added.
We need a better solution, e.g.:

• creating a formal registry of validators the Orch cannot run directly
• checking whether the validator's implementation exists in the builtin definitions
• add a flag to the validator ZObject itself(?!)

(this is the followup from https://phabricator.wikimedia.org/T426335