Observability example: Enhance with more scenarios

The observability example is doing a great jobs.
Some users faced situations where they needed more scenarios, like:
+ Hide metrics
+ Show metrics
+ Use custom metrics

Maybe this is not Camel Quarkus specific, in which case pointing to existing docs outside Camel would be enough.

Start by locating the observability example and reviewing its existing documentation and scenarios. Determine whether hide-metrics, show-metrics, and custom-metrics guidance belongs in Camel Quarkus or should link to existing Camel documentation. Done means the requested scenarios are documented in the appropriate location.

Written by the indexing model from the issue text.