add option to enable Service Monitor deployment

[maratsal]

Is your feature request related to a problem? Please describe.
Currently operator supports deployment of prometheus instance within argocd object deployment. It would be great to have option to enable deployment of just service monitors to collect metrics by existing prometheus installation on the cluster.

Describe the solution you'd like
would be something like this:

apiVersion: argoproj.io/v1alpha1
kind: ArgoCD
metadata:
  name: example-argocd
  labels:
    example: insights
spec:
  metrics:
    serviceMonitor:
      enabled: true

or more granularly

apiVersion: argoproj.io/v1alpha1
kind: ArgoCD
metadata:
  name: example-argocd
  labels:
    example: insights
spec:
  metrics:
    serviceMonitor:
      applicationController:
        enabled: true
      apiServer:
        enabled: true
      repoServer:
        enabled: true

Describe alternatives you've considered
currently deploying service monitors separately along with argo cd.

Additional context
N/A

[Morriz]

Would be awesome. Not much work to implement ;)

[iam-veeramalla]

@jopit What do you think about this one ?