Support adopting existing radosgw buckets and users

The operator previously assumed it created every user and bucket it managed:
reconciling an existing resource could overwrite its user attributes or wipe its
bucket policy, and deleting a CRD always deleted the underlying RGW object (only
Bucket had retainOnDelete). That made taking over pre-existing radosgw state
unsafe. Make adoption first-class.

- add retainOnDelete to ObjectStoreUser and BucketAccess (dedicated users), so
  deleting the CRD orphans the RGW user instead of deleting it (symmetric with
  Bucket)
- merge bucket policy instead of replacing it: the operator marks its own
  statements with a cephrgwop* Sid and preserves any statement it does not own,
  so adopting a bucket with a hand-written policy keeps it; add Bucket
  managePolicy (default true) to opt out of policy management entirely
- only reconcile user attributes the spec sets: DisplayName when non-empty and
  Suspended is now an optional *bool, so adopting a user does not reset them
- record adoption: ObjectStoreUser/Bucket status.adopted (+ printcolumn) is true
  when the RGW object already existed on first reconcile
- add GetBucketPolicy + MergeBucketPolicy; keyed adoption detection off the
  status identity field so a Pending owner wait does not mislabel it
- regenerate CRDs/deepcopy; add docs/adoption.md and
  config/samples/05-adoption.yaml; cover the merge in policy_test.go

Claude-Session: https://claude.ai/code/session_016CEncETbf8cvy1PhsHfFHM

internal/controller/bucketaccess_controller.go

@@ -49,8 +49,9 @@ func (r *BucketAccessReconciler) Reconcile(ctx context.Context, req ctrl.Request
 
 	if !ba.DeletionTimestamp.IsZero() {
 		if controllerutil.ContainsFinalizer(&ba, finalizer) {
-			// Only delete a user the operator created for this grant.
-			if managed && uid != "" {
+			// Only delete a user the operator created for this grant, and only
+			// when the grant does not ask to retain it.
+			if managed && uid != "" && !ba.Spec.RetainOnDelete {
 				if err := r.Ceph.DeleteUser(ctx, uid); err != nil {
 					return r.fail(ctx, &ba, "DeleteFailed", err)
 				}