Add image role, support logging in to registries

roles/service/meta/argument_specs.yaml

@@ -35,6 +35,23 @@ argument_specs:
         description: "The image to run in the service container(s), in FQIN format (registry/imagename:tag)."
         type: str
         required: true
+      service_container_image_creds:
+        description: Credentials used to authenticate with the registry
+        type: dict
+        required: false
+        default:
+          username: ""
+          password: ""
+        options:
+          username:
+            description: Username
+            type: str
+            required: true
+          password:
+            description: Password
+            type: str
+            required: true
+
       service_container_user:
         description: The UID to run as inside the container
         type: str