helm: allow setting priorityClassName on the operator deployment

[rewantsoni]

Describe what this PR does

Allow setting priorityClassName on operator deployment via controllerManager.priorityClassName

Related issues

Fixes: #450

Checklist:

• Commit Message Formatting: Commit titles and messages follow
  guidelines in the developer guide.
• Reviewed the developer guide on Submitting a Pull Request
• Pending release notes updated with breaking and/or notable changes for the next major release.
• Documentation has been updated, if necessary.
• Unit tests have been added, if necessary.
• Integration tests have been added, if necessary.

[rewantsoni]

Tested the changes by

helm template test deploy/charts/ceph-csi-operator/  --set controllerManager.priorityClassName=system-cluster-critical
---
# Source: ceph-csi-operator/templates/deployment.yaml
apiVersion: apps/v1
kind: Deployment
metadata:
  name: test-ceph-csi-operator-controller-manager
  namespace: default
  labels:
  ...
spec:
  ...
  template:
    metadata:
    ...
    spec:
      containers:
      - args:
      ....
      serviceAccountName: test-ceph-csi-operator-controller-manager
      terminationGracePeriodSeconds: 10
      priorityClassName: system-cluster-critical

[Madhu-1]

@rewantsoni how about adding empty value for manager.yaml will that works?

[rewantsoni]

Adding empty value for priorityClassName would make the kubebuilder add the priorityClassName field to the bundle (deploy/all-in-one/install.yaml has the field), but one we helmify it the field it removed from the deployment.yaml (charts/ceph-csi-operator/deploymeny)