events schema: separate individual event type definitions from definition of event collection?

[infotroph]

Comment by @infotroph in #3621 (comment) :

I ask this without looking at the rules for JSON schema specs, so apologies if the answer is "this is how it has to work". BUT:

One list of all the possible properties of every event type feels like it will get unmanageable really fast as we add more event types. Is there a way to enumerate the possible event types here without any of their internal details, and then elsewhere in the schema have each event type get its own separate definition of only the properties accepted by that type?