Remove version pinned Prometheus operator

Overview

When upgrading the Prometheus Operator in https://gitlab.com/gitlab-com/gl-infra/infrastructure/-/issues/13973 we had to use a specific SHA since we required a fix that wasn't tagged yet.

This was done in gitlab-com/gl-infra/k8s-workloads/gitlab-helmfiles!499 (merged) specifying the image keyword

Proposal

• Wait for https://github.com/prometheus-operator/prometheus-operator to release a new tag

• Check which tag provides https://github.com/prometheus-operator/prometheus-operator/commit/0a38647379a5e93f639bf8e634deabcc32e01fb6 by running git describe --contains "0a38647379a5e93f639bf8e634deabcc32e01fb6"

• When a new release is cut, use that tag instead of master@sha

• Update README to specify the correct CRD

• Update the CRDs to a specific tag as well

  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_alertmanagerconfigs.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_alertmanagers.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_podmonitors.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_probes.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_prometheuses.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_prometheusrules.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_servicemonitors.yaml
  kubectl apply -f https://raw.githubusercontent.com/prometheus-operator/prometheus-operator/$TAG/example/prometheus-operator-crd/monitoring.coreos.com_thanosrulers.yaml