Disable traces and metrics

[morozovcookie]

I need to add an options for disabling traces and metrics for the client and server separately. Names for those parameters will be -no-client-traces, -no-server-traces, -no-client-metrics and -no-server-metrics.

First of all this need to me to disable traces and metrics on code generating stage. I know that I can pass NoopTracer from the client code which will use this library, but why? If I know I don't need this code, I just need to be able to turn it off.

Usecase for that. I want to have the monitor server (liveness, readiness, etc.) and API server with the same code base. With current configuration I will get monitor server with traces and metrics. I no need this. I want statically generate the server and use it in every service.

Secondly, I do not like how it designed, so I want to rewrite it for myself in the next issue. NOTE: that could be done with middleware not for the Handler, but for the standard http.Handler.