Metrics-server: Revise prometheus metrics

[serathius]

As suggested by @s-urbaniak in https://github.com/kubernetes-sigs/metrics-server/pull/387
We should leverage the best practices we defined in https://github.com/kubernetes/enhancements/blob/master/keps/sig-instrumentation/20181106-kubernetes-metrics-overhaul.md#motivation and start dependency injecting the prometheus registry into components.

/kind feature

[serathius]

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[serathius]

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[serathius]

@s-urbaniak
Having quality metrics is very important for next release. I added this issue to v0.4.0 milestone, that I will be preparing to release in near feature.
Will you be able to work on this?

[s-urbaniak]

@serathius yeah, i'll give it a spin! :tada:

[s-urbaniak]

We have precendences in the eco-system on how to dependency-inject registries in kubelet [1]. I will work towards that idiom.

[1] https://github.com/kubernetes/kubernetes/blob/master/pkg/kubelet/server/server.go#L389-L394

[s-urbaniak]

cc @dgrisonnet how do you feel of tackling this one? :-)

[dgrisonnet]

Sounds interesting, I can give it a try :)