Implement default resource modifier in restore controller

Thread DefaultResourceModifierConfigMap from server config through to
restoreReconciler. Refactor validateAndComplete to use a shared
loadResourceModifierConfigMap helper that handles both default and
per-restore ConfigMap loading.

Precedence: per-restore modifier takes exclusive precedence over the
default. Default ConfigMap errors are non-fatal (warn and proceed).
SkipDefaultResourceModifier opt-out is respected.

Includes unit tests covering: default-only, per-restore override,
skip flag, missing default (non-fatal), missing per-restore (fatal),
and no modifier configured.

Signed-off-by: Shubham Pampattiwar <spampatt@redhat.com>

pkg/cmd/server/server.go

@@ -881,6 +881,7 @@ func (s *server) runControllers(defaultVolumeSnapshotLocations map[string]string
 			s.config.DisableInformerCache,
 			s.crClient,
 			s.config.ResourceTimeout,
+			s.config.DefaultResourceModifierConfigMap,
 		)
 
 		if err = r.SetupWithManager(s.mgr); err != nil {