fix: Allow override of default /tmp volume mount in repo server

[jgwest]

What type of PR is this?
/kind bug

What does this PR do / why we need it:

The ArgoCD HA guidelines [1] says:

argocd-repo-server clones the repository into /tmp (or the path specified in the TMPDIR env variable). The Pod might run out of disk space if it has too many repositories or if the repositories have a lot of files. To avoid this problem mount a persistent volume.

However, with the current behaviour of argocd-operator, it is not possible to override the tmp path: when you attempt to do so, you will see this error in the operator logs:

2024-07-16T07:32:47Z ERROR Reconciler error {"controller": "argocd", "controllerGroup": "argoproj.io", "controllerKind": "ArgoCD", "ArgoCD": {"name":"argocd","namespace":"jgw"}, "namespace": "jgw", "name": "argocd", "reconcileID": "6979a388-fdae-453d-b999-b026aa1e260b", "error": "Deployment.apps \"argocd-repo-server\" is invalid: spec.template.spec.containers[0].volumeMounts[8].mountPath: Invalid value: \"/tmp\": must be unique"}
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).reconcileHandler
/remote-source/deps/gomod/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.2/pkg/internal/controller/controller.go:329
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).processNextWorkItem
/remote-source/deps/gomod/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.2/pkg/internal/controller/controller.go:266
sigs.k8s.io/controller-runtime/pkg/internal/controller.(*Controller).Start.func2.2
/remote-source/deps/gomod/pkg/mod/sigs.k8s.io/controller-runtime@v0.17.2/pkg/internal/controller/controller.go:227
W0716 07:33:31.475998 1 warnings.go:70] apps.openshift.io/v1 DeploymentConfig is deprecated in v4.14+, unavailable in v4.10000+

using an ArgoCD CR like this:

kind: ArgoCD
# (...)
spec:
  # (...)
  repo:
    resources:
      limits:
        cpu: '1'
        memory: 1Gi
      requests:
        cpu: 250m
        memory: 256Mi
    volumeMounts:
      - mountPath: /tmp
        name: my-volume
    volumes:
      - emptyDir: {} # in practice, a user would likely use a persistent volume for increased storage capacity
        name: my-volume

This PR skips creation of the default /tmp mount path in the case where the user is already providing one via .spec.repo.volumeMounts in the ArgoCD CR.

Have you updated the necessary documentation?

• Documentation update is required by this PR.
• Documentation has been updated.

Which issue(s) this PR fixes:
N/A

How to test changes / Special notes to the reviewer:

[jgwest]

Red Hat tracking JIRA: https://issues.redhat.com/browse/GITOPS-4602

[jgwest]

Failed on:
--- FAIL: kuttl/harness/1-036_validate_role_rolebinding_for_source_namespace (63.91s)

[svghadi]

LGTM. Thanks @jgwest. I have same exact fix for one the issue I am working on 😆. If you can rebase we can get this in.

[svghadi]

Thanks. Will merge it.