[v2] Annotation Autodiscovery improvements

[petewall]

Some improvements to the annotationAutodiscovery feature:

• Have a switch to enable/disable pods or services:

pods:
  enabled: true

services:
  enabled: true

• Make it easy to set static labels and extract common labels:

pods:
  labels:
    pod: __meta_kubernetes_pod_name
    namesapace: __meta_kubernetes_namespace
    node: __meta_kubernetes_pod_node_name
    region: __meta_kubernets_pod_label_region
  staticLabels:
    color: red

• Add the ability to extract __param_<key>__ parameters:

annotations:
  metricsScrapeParams: k8s.grafana.com/metrics.param.

Which would set:

    rule {
      action = "labelmap"
      regex = "__meta_kubernetes_pod_annotation_k8s_grafana_com_metrics_param_(.+)"
      replacement = "__param_$1"
    }

• Add label matchers to better filter pods and services:

labelMatchers:
  region: us
pods:
  labelMatchers:
    color: blue

will result in:

discovery.kubernetes "pods" {
  role = "pod"
  selectors {
    role = "pod"
    label = "region=us,color=blue"
  }
}

This is more efficient that filtering in the discovery.relabel section. It could be, and should be, unique per pods and services.