Make Metrics extension use Vert.x instead of Servlets

[gsmet]

Per discussion with @jmartisk .

See this PR #4062 for some examples.

[gastaldi]

That looks interesting. May I give it a try or is this already being worked on by someone else?

[jmartisk]

I'm planning to do that, per discussion in #4151 if you don't mind :) yeah it does sound like an interesting task. I suppose there must be some more extensions that still need the same

[gastaldi]

I'm planning to do that, per discussion in #4151 if you don't mind :)

@jmartisk not at all, by all means 😉

@gsmet can this issue be assigned to @jmartisk ?

[geoand]

Does is make sense to open a similar issue for Opentracing? That one relies on servlets in the way of providing a Servlet filter.