Custom API Hook for Relational Triggers Information Missing

### Describe the Request

So as in https://github.com/directus/directus/issues/2942 and in https://github.com/directus/directus/discussions/13392
it comes to the point, that when creating a custom api hook as defined in (https://docs.directus.io/extensions/hooks.html) the hook will not be called. So the custom api hook doc is here misleading as this case is not covered.

### Maintenance Strategy

I would suggest:
- A) Either add the information that relational triggers will not cause custom api hooks to be called or
- B) Add the support for that