Trigger Server Counters usage API whenever a deprecation is triggered

[afharo]

Describe the feature:
In order to help us with identifying when deprecated features are no longer used, it would be interesting to know how many times each deprecation warning is triggered.

A hook and a usage collector could help with this.

Describe a specific use case for the feature:
We may want to track deprecation notifications for

• HTTP Headers (related to [core.http] Support Warning headers for deprecated http routes #105692)
• Configuration
• Other plugin APIs

[elasticmachine]

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

[elasticmachine]

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

[pgayvallet]

We may want to track deprecation notifications for

HTTP Headers

It's more tracking the hits on any deprecated HTTP endpoint, right? This totally makes sense to me.

Ideally, we should automate this from core once we're allowed to flag an API as deprecated.

Configuration

You mean everytime a config value is accessed? That may be very tricky, especially because some props are exposed to the browser, where it would be very hard to track (but even on the server, it's far from trivial)

Other plugin APIs

This one can't probably be automated, to having an API for plugin owners to manually call probably makes sense.

[afharo]

You mean everytime a config value is accessed? That may be very tricky, especially because some props are exposed to the browser, where it would be very hard to track (but even on the server, it's far from trivial)

I was thinking more about when logging a deprecated config item.

We could, probably, put it together to the Other plugin APIs bit. Core could provide a deprecation log, and we could emit an event for every log entry to that logger?

[lukeelmers]

With existing deprecation logs & with the possibility of future event based telemetry, we don't think this issue is needed anymore.