fix(shared): Make sure labels aren't unintentionally dropped

The first patch that "adds" `{}` to `/metadata/labels` would replace any
existing labels resulting in unexpected behaviour. Instead we rely on
the preexistence of the labels field in the namespace.

apps/base/findmydevice/namespace.yaml

@@ -2,3 +2,4 @@ apiVersion: v1
 kind: Namespace
 metadata:
   name: findmydevice
+  labels: {}

apps/base/forecastle/namespace.yaml

@@ -2,3 +2,4 @@ apiVersion: v1
 kind: Namespace
 metadata:
   name: forecastle
+  labels: {}

shared/components/namespace-baseline/namespace.yaml

-- op: add
-  path: /metadata/labels
-  value: {}
 - op: add
   path: /metadata/labels/pod-security.kubernetes.io~1audit
   value: restricted

shared/components/namespace-restricted/namespace.yaml

-- op: add
-  path: /metadata/labels
-  value: {}
 - op: add
   path: /metadata/labels/pod-security.kubernetes.io~1audit
   value: restricted