[APM] Deprecation of the Watcher error reporting feature

[formgeist]

Summary

As per #70324 we're choosing to remove the enable error reports Watcher integration from our integration options in the APM app. We're no longer committed to support creating new Watcher error reports as they can be in many ways to replicated by the new threshold alerts supported by our Alerting integration and we could easily supply Watcher-aficionado's the option to create the reports by using a Watcher recipe.

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)