Move collectors defined in the telemetry plugin out of it

[afharo]

There are a few general collectors defined in the telemetry plugin: https://github.com/elastic/kibana/tree/452193fdba7c77815472889d1715b1ca341530ba/src/plugins/telemetry/server/collectors

We should extract them from this plugin because these collectors are also used by the monitoring plugin when retrieving Kibana stats (for monitoring purposes, not telemetry) and if telemetry.enabled: false, we won't register these collectors

[elasticmachine]

Pinging @elastic/pulse (Team:Pulse)

[TinaHeiligers]

@afharo would you consider this a bug or a normal issue from changes that happen over releases? I assume the priority is fairly high.

[afharo]

I'd say to fix it ASAP. But I doubt it needs to be included in patch releases. I think targeting it for 7.9 should be enough.

It's also a very simple one: simply move the collectors to another plugin (either to a new plugin kibana_usage_collectors that can be maintained by the NP/core team in the future or to the usage_collection itself since they are core collectors). I can create a PR today.