CHORE(grafana): remove admin login secret for SSO

- Remove grafana-admin-password ExternalSecret
- Remove admin section from helm-values.yaml
- Authentication handled by Authelia SSO middleware

grafana/manifests/secret.yaml

@@ -1,28 +1,5 @@
 apiVersion: external-secrets.io/v1
 kind: ExternalSecret
-metadata:
-  name: grafana-admin-password
-  namespace: grafana
-spec:
-  refreshInterval: 1h
-  secretStoreRef:
-    kind: ClusterSecretStore
-    name: vault-backend
-  target:
-    name: grafana-admin-password
-    creationPolicy: Owner
-  data:
-    - secretKey: admin-user
-      remoteRef:
-        key: grafana
-        property: ADMIN_USER
-    - secretKey: admin-password
-      remoteRef:
-        key: grafana
-        property: ADMIN_PASSWORD
----
-apiVersion: external-secrets.io/v1
-kind: ExternalSecret
 metadata:
   name: grafana-db-password
   namespace: grafana