better CA trust support for repo server

[davidkarlsen]

Is your feature request related to a problem? Please describe.
I have to add the following to argocd cr:
spec.repo:

 repo:
      env:
      - name: SSL_CERT_DIR
        value: /tmp/sslcertdir
     - mountPath: /tmp/sslcertdir
        name: ssl
      volumes:
      - configMap:
          name: user-ca-bundle
        name: ssl

for it to avoid TLS errors when talking our git host. The cert in question is signed by the bundle already added to the OCP Proxy object. This isn't very polished.

Describe the solution you'd like
Two things:

1. be able to refer to a configmap or secret containing a bundle
2. to trust the bundle that is already defined in the OCP Proxy (k get proxy cluster -o yaml)

Describe alternatives you've considered
The above more intrusive method.

Additional context
argoproj/argo-cd#3539 (comment)