Generate API method to check subscription requirements

[johanv]

I want a Kavo.validateparticipant API with params contact_id, event_id and role_id, that checks whether the contacts can subscribe with given role to the given event.

[johanv]

Here are the specs for participants:

A: Je wordt 16 jaar of ouder in het jaar van de cursus.
HA: Je wordt 18 jaar of ouder en je hebt al minstens een jaar leidingservaring.
I: Je wordt 19 jaar of ouder en je hebt de competenties van een animator.

The 'leidingservaring' should be checked using a hook, because it will depend on how this is configured in CiviCRM. (It would probably better to inject the leidingservaring as a dependency, but I'm not sure how this works in CiviCRM).

[johanv]

I think I should create a ParticipantWorker and implement Worker::canCreate.

I think will create a ParticipantWorker and implement Worker::validateKavo. (Don't call it canCreate, because it will get confusing because there is also an unrelated Worker::create function.)