Only own and reconcile Prometheus if supported

What does this MR do?

Only own and reconcile Prometheus if supported

If the Prometheus API is available in `monitoring.coreos.com/v1`, then
own Prometheus objects.

If Prometheus is enabled in the configuration, it will reconcile related
objects.

Closes
https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/issues/339

Changelog: fixed

Checklist

See Definition of done.

For anything in this list which will not be completed, please provide a reason in the MR discussion.

Required

• Merge Request Title and Description are up to date, accurate, and descriptive
• MR targeting the appropriate branch
• MR has a green pipeline on GitLab.com
• When ready for review, MR is labeled "~workflow::ready for review" per the Distribution MR workflow

Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Tests added
• Integration tests added to GitLab QA
• Equivalent MR/issue for omnibus-gitlab opened
• Validate potential values for new configuration settings. Formats such as integer 10, duration 10s, URI scheme://user:passwd@host:port may require quotation or other special handling when rendered in a template and written to a configuration file.

Related issues

Closes #339 (closed)

Test plan

Without Prometheus API available

1. TAG=339-prometheus-condition task build_operator

2. task deploy_operator

3. Confirm that there is no message about owning Prometheus:

   $ stern -n gitlab-system -l control-plane=controller-manager -i Prometheus
   + gitlab-controller-manager-6fb664b4c8-bn5xh › kube-rbac-proxy
   + gitlab-controller-manager-6fb664b4c8-bn5xh › manager

With Prometheus API available

1. Install Prometheus CRDs:

   $ LATEST=$(curl -s https://api.github.com/repos/prometheus-operator/prometheus-operator/releases/latest | jq -cr .tag_name)
   
   $ curl -sLO https://github.com/prometheus-operator/prometheus-operator/releases/download/${LATEST}/bundle.yaml
   
   $ kubectl apply -f bundle.yaml --server-side # needed this flag to avoid error about annotations being too long
   ...
   
   $ kubectl api-resources | grep -i prometheus
   prometheusagents                  promagent    monitoring.coreos.com/v1alpha1         true         PrometheusAgent
   prometheuses                      prom         monitoring.coreos.com/v1               true         Prometheus
   prometheusrules                   promrule     monitoring.coreos.com/v1               true         PrometheusRule

2. Restart the Operator Pod by deleting it.

3. Watch the logs and confirm it owns Prometheus:

   $ stern -n gitlab-system -l control-plane=controller-manager -i Prometheus
   + gitlab-controller-manager-5445f78774-m8sdr › kube-rbac-proxy
   + gitlab-controller-manager-5445f78774-m8sdr › manager
   gitlab-controller-manager-5445f78774-m8sdr manager 2023/07/11 22:04:38 mitchdebug: comparing: Probe Prometheus
   gitlab-controller-manager-5445f78774-m8sdr manager 2023/07/11 22:04:38 mitchdebug: comparing: Prometheus Prometheus
   gitlab-controller-manager-5445f78774-m8sdr manager 2023-07-11T22:04:38Z INFO    controllers.GitLab      Using monitoring.coreos.com/v1/Prometheus
   gitlab-controller-manager-5445f78774-m8sdr manager 2023-07-11T22:04:54Z INFO    Starting EventSource    {"controller": "gitlab", "controllerGroup": "apps.gitlab.com", "controllerKind": "GitLab", "source": "kind source: *v1.Prometheus"}