[Telemetry] Deprecate telemetry url configs

[Bamieh]

We have no useful cases for changing the actual telemetry urls for deployments.

I suggest we deprecate the telemetry url configs (telemetry.url and telemetry.optInStatusUrl) in favor of a telemetry.staging: boolean config. The url paths will be handled internally by the service.

This would be a breaking change for 8.0.0. We'd need to propogate this change internally as well across our testing environments.

[elasticmachine]

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

[elasticmachine]

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

[pgayvallet]

@Bamieh should we add this to #84380?

[afharo]

We need to sync with the QA and Cloud teams as they are setting those configs when deploying dev, QA and staging deployments.

[Bamieh]

Ahh too many meta issues 🙃 I've added it. @afharo yes we need to communicate this breaking change along with all the other breaking changes we'll be shipping in 8.0

[TinaHeiligers]

We need to sync with the QA and Cloud teams as they are setting those configs when deploying dev, QA and staging deployments.

@Bamieh did you sync with QA and the Cloud teams while you were working on #107396?