Take over agent configs

[QuentinBisson]

What this PR does / why we need it

This PR takes over the remote write configuration from prometheus-meta-operator if mimir is enabled

Checklist

• Update changelog in CHANGELOG.md.

[QuentinBisson]

Configmap testing:

PMO CM:

k get cm -n org-giantswarm golem-remote-write-config -oyaml
apiVersion: v1
data:
  values: |
    global: {}
    prometheus-agent:
      externalLabels:
        cluster_id: golem
        cluster_type: management_cluster
        customer: giantswarm
        installation: golem
        organization: giantswarm
        pipeline: testing
        provider: capa
        region: eu-west-2
        service_priority: highest
      image:
        tag: v2.50.1
      shards: 1
      version: v2.50.1
kind: ConfigMap
metadata:
  creationTimestamp: "2023-05-09T13:34:16Z"
  finalizers:
  - observability.giantswarm.io/monitoring
  labels:
    app-operator.giantswarm.io/watching: "true"
  name: golem-remote-write-config
  namespace: org-giantswarm
  resourceVersion: "1006002975"
  uid: 16a0ff42-0365-4511-a443-cccf876a9416

Then edited by observability-operator:

k get cm -n org-giantswarm golem-remote-write-config -oyaml
apiVersion: v1
data:
  values: |
    prometheus-agent:
      externalLabels:
        cluster_id: golem
        cluster_type: management_cluster
        customer: giantswarm
        installation: golem
        organization: giantswarm
        pipeline: testing
        provider: capa
        region: eu-west-2
        service_priority: highest
      image:
        tag: v2.51.1
      shards: 1
      version: v2.51.1
kind: ConfigMap
metadata:
  creationTimestamp: "2023-05-09T13:34:16Z"
  finalizers:
  - observability.giantswarm.io/monitoring
  labels:
    app-operator.giantswarm.io/watching: "true"
  name: golem-remote-write-config
  namespace: org-giantswarm
  resourceVersion: "1006007639"
  uid: 16a0ff42-0365-4511-a443-cccf876a9416

[QuentinBisson]

This now uses Mimir

[QuentinBisson]

Uses the active series in agents instead of prometheus tsdb head series so we can get rid of the MC proms

[QuentinBisson]

Currently configured to send to be .installationName.baseDomain but