Add provider field to nginx and gloo docs

docs/gitbook/usage/gloo-progressive-delivery.md

@@ -103,6 +103,7 @@ metadata:
   name: podinfo
   namespace: test
 spec:
+  provider: gloo
   # deployment reference
   targetRef:
     apiVersion: apps/v1

docs/gitbook/usage/nginx-progressive-delivery.md

@@ -104,6 +104,7 @@ metadata:
   name: podinfo
   namespace: test
 spec:
+  provider: nginx
   # deployment reference
   targetRef:
     apiVersion: apps/v1