Add flux create secret receiver command

Signed-off-by: Stefan Prodan <stefan.prodan@gmail.com>

cmd/flux/testdata/create_secret/receiver/secret-receiver-gcr.yaml

@@ -0,0 +1,13 @@
+---
+apiVersion: v1
+kind: Secret
+metadata:
+  annotations:
+    notification.toolkit.fluxcd.io/webhook: https://flux.example.com/hook/6d6c55e9affb9d1e0d101ce604ae4270880ec1ff24d1bd2d928fcd64243d21a4
+  name: gcr-secret
+  namespace: my-namespace
+stringData:
+  audience: https://flux.example.com/hook/6d6c55e9affb9d1e0d101ce604ae4270880ec1ff24d1bd2d928fcd64243d21a4
+  email: sa@project.iam.gserviceaccount.com
+  token: test-token
+