[HTTP] Log deprecated API usages

[jloleysens]

Since we now track deprecated Kibana API usage (#196081) we should also create a (debug) log to help track down origins of requests.

We should have Kibana configuration for turning on this logging in a way that does not flood log output with all HTTP req/res traffic and instead only surfaces deprecations - similar to what we do when detecting deprecated ES API requests from Kibana (code).

We should be able to use existing debug logging logic for these new debug logs.

Additionally, API integrations should be able to send a user-provided value that we can surface when this logging is activated to provide the best experience for tracking down origins of deprecated usage.

Part of implementation: we should also surface this in public docs.

Open questions:

• Do we want to ask users to send a x-opaque-id (similar to ES) to provide the "user input" for the log?

[elasticmachine]

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