[UsageCollection] Create `StatsCollector` as an extension of `Collector`

[afharo]

An aside: We're being explicit about defining a different UsageCollector class from the Collector class and I wonder if it would be more consistent if we had a base Collector class and extended it to a new StatsCollector class even if we're not actually extending the Collector 🤔

Originally posted by @TinaHeiligers in #83413 (comment)

[elasticmachine]

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

[TinaHeiligers]

Thanks for creating this issue @afharo !
I don't think it's urgent and probably doesn't need to happen for 7.11. You certainly have other work that's higher priority.
We can add this ticket to the planning session.

[elasticmachine]

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

[afharo]

Closing the issue for now. The reasons are in this discussion: #85554 (comment)

We can revisit it whenever we actually need a differentiation 🙂