Support installing/configuring metrics-server

[slashpai]

What is missing?

Currently only prometheus-adapter is supported which is the resource metrics api implementation. A light weight implementation of same metrics-server is not supported.

currently https://github.com/prometheus-operator/kube-prometheus/tree/main/experimental/metrics-server is provided which is not configurable.

add metrics-server in https://github.com/prometheus-operator/kube-prometheus/tree/main/jsonnet/kube-prometheus/components

Why do we need it?

For someone who uses keda for autoscaling on custom metrics prometheus adapter may be overhead as it may be required only for resource metrics API. Instead of having it as the only option it would be useful to have flag set if we need to configure prometheus-adapter/metrics-server and default can be prometheus-adapter as its currently installed. This would allow users to chose between two resource metrics api implementations.

Environment

NA

• kube-prometheus version:

  Insert Git SHA here

Anything else we need to know?:

Since keda is getting lot of traction, prometheus-adapter will be deprecated in near future. It would be good to have alternate implementation supported in kube-prometheus

cc: @simonpasquier @dgrisonnet