feat: Support notifications in any namespace

[nmirasch]

What type of PR is this?

/kind enhancement

What does this PR do / why we need it:
Adding support for the Operator to be able to use ArgoCD in Any Namespaces with The Notification Controller. Support upstream Argo CD in any namespace feature in operator https://argo-cd.readthedocs.io/en/stable/operator-manual/notifications/#namespace-based-configuration

Which issue(s) this PR fixes:

Fixes https://issues.redhat.com/browse/GITOPS-8026 & https://issues.redhat.com/browse/GITOPS-8025

[svghadi]

Can have the cleanup logic similar to #1209 for consistency?

[svghadi]

Thanks @nmirasch for the PR. While testing, I ran into below error

Example:

apiVersion: argoproj.io/v1beta1
kind: ArgoCD
metadata:
  name: test
spec:
  sourceNamespaces:
    - apps
  notifications:
    enabled: true
    sourceNamespaces:
      - apps

Error

- lastTransitionTime: "2025-10-29T04:49:07Z"
    message: |-
      failed to create rolebinding test-default-notifications in namespace apps
      RoleBinding.rbac.authorization.k8s.io "test-default-notifications" is invalid: roleRef.apiGroup: Unsupported value: "meta.k8s.io": supported values: "rbac.authorization.k8s.io"
    reason: ErrorOccurred

[nmirasch]

@svghadi code updated!

[svghadi]

I was wondering if we should consider creating a NotificationsConfiguration CR in the source namespaces as well, similar to what we do in the Argo CD instance namespace. This would provide a consistent UX where users manage the argocd-notifications-cm ConfigMap through the NotificationsConfiguration CR instead of editing the ConfigMap directly.

[svghadi]

Overall looks good. Left few comments.

[svghadi]

LGTM. Thanks.

[svghadi]

Merging this one. Let's add e2e and docs in separate PR.