AppD v2 routes don't define error response samples

[kriswest]

Minor Issue

AppD v2 routes don't define error responses in their OpenAPI definitions. The endpoint for retrieving a single appD record should at least define a 404 to be returned when the appId is not found.

AppD v2 routes don't include error response samples, which should be added to the OpenAPI definitions to make the expected error responses clearer.

Area of Issue

[x] App Directory