Allow more complete configuration of Dex

Is your feature request related to a problem? Please describe.
When configuring Dex it seems that there's only a limited amount of configuration available in the operator. E.g., if I want to utilize Google Workspace and at the same time groups I need to do some additional setups of a secret and linking that to the argocd-dex-server. A task that logically - at least if you ask me - should be done by the operator

Describe the solution you'd like
I'd like a way to configure the argocd-dex-server with additional settings, such as those described here: https://argo-cd.readthedocs.io/en/stable/operator-manual/user-management/google/#configure-dex

One way of configuring it could be:

apiVersion: argoproj.io/v1alpha1
kind: ArgoCD
metadata:
  name: argocd
spec:
  dex:
    config: |
      connectors:
        - id: google
          name: ..

  dex-server:
    oicd:
        googleAuth: |
            { /* ... my json here ... */ }

[gnanderson]

@rfftrifork I just came across this limitation, as a work around I deployed a simple Kyverno mutating policy:

apiVersion: kyverno.io/v1
kind: Policy
metadata:
  name: argocd-dex-google-credentials
  namespace: argocd
  annotations:
    policies.kyverno.io/title: Mutate ArgoCD dex deployment
    policies.kyverno.io/subject: Deployment
    policies.kyverno.io/description: >-
      Adds a volume mount to the dex deployment to mount the google credentials json.
      This json is used for dex to authenticate and query Google workspace directory 
      for a user's groups. You may then use these groups in ArgoCD RBAC.
spec:
  validationFailureAction: enforce
  rules:
    - name: set-argocd-dex-google-credentials
      match:
        resources:
          kinds:
            - apps/v1/Deployment
          names:
            - argocd-dex-server
      mutate:
        patchStrategicMerge:
          spec:
            template:
              spec:
                containers:
                  - name: dex
                    volumeMounts:
                      - name: google-groups-credentials
                        mountPath: /etc/google/groups-credentials
                        readOnly: true
                volumes:
                  - name: google-groups-credentials
                    secret:
                      defaultMode: 420
                      secretName: argocd-google-groups-credentials