[Telemetry] [Collectors] Application Usage: Define collector.schema

[afharo]

In order to complete #70180, we should define the collector schema for the collector "Application Usage".

The added complexity here is that it is not static and it depends on the values set as id when the plugins register Kibana applications via the method core.application.register.

Maybe we can come up with a parser that can collect all the places where that method is called and builds up the schema for us?

[elasticmachine]

Pinging @elastic/kibana-telemetry (Team:KibanaTelemetry)

[TinaHeiligers]

@afharo once this issue is resolved (PR for it merged), please remember to check it off the list in #70180

[afharo]

I've created #75329 to track the possible idea of generating the schema dynamically by some process that would identify all the IDs in the use of the method core.application.register.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)