Add documentation for metrics

[lilic]

We should have more documentation about how to best handle metrics and how to use the ExposeMetricsPort() and GenerateServiceMonitor() helper functions.

Currently blocked until metrics PR land in controller-runtime.

[primeroz]

@lilic Is anything happening on this documentation ? I might have just misunderstood the whole thing but an operator I use was updated to version "0.6.0" of the sdk and looking at the operator-sdk release notes and #786 It should now expose Metrics

kubectl logs vault-operator-5df59cfdff-99t4p | grep sdk   
{"level":"info","ts":1554476387.2531166,"logger":"cmd","msg":"operator-sdk Version: v0.6.0"}

I can see port 8080 listening but i get no metrics out of it

~ $ wget localhost:8080/metrics -O-
Connecting to localhost:8080 (127.0.0.1:8080)

~ $

Is there anything i need to do to get those metrics ?

[lilic]

@primeroz Hello, there is already documentation, I guess we forgot to close this issue. Default metrics are exposed on port :8383. Let me know if this works or if you are running into any more problems.

https://github.com/operator-framework/operator-sdk/tree/master/doc/user/metrics