Add app.kubernetes.io/part-of: flux label

To be used in a future version of Flux to better select Flux components
in a namespace, as the namespace value for the
`app.kubernetes.io/instance` could be used by non Flux related
workloads.

Signed-off-by: Hidde Beydals <hello@hidde.co>

pkg/manifestgen/install/templates.go

@@ -154,6 +154,7 @@ metadata:
 labels:
   app.kubernetes.io/instance: {{.Namespace}}
   app.kubernetes.io/version: "{{.Version}}"
+  app.kubernetes.io/part-of: flux
 fieldSpecs:
   - path: metadata/labels
     create: true