Consider integrating Jetty/Dropwizard metrics

Once the basic new INFRAUTILS-19 metrics is fully done and dusted, it could be useful to see how hard it would be to use http://metrics.dropwizard.io/3.1.0/manual/jetty/ to get metrics for the ODL Jetty HTTP server used e.g. by RESTCONF.

Similarly, if we use Jersey for REST APIs in ODL (do we?) then http://metrics.dropwizard.io/3.1.0/manual/jersey/ looks interesting.

I expect with Karaf OSGi and all, this may be a little more challenging than in some plain Spring Boot or whatever environment.

It depends on how we actually do Web stuff in ODL.. do we rely on OSGi Web support, or directly use the Jetty APIs?