Err embedding when multiple relationships found

When having one-to-many relationships like:

person        -< message[sender]
person        -< message[recipient]
person_detail -< message[sender]
person_detail -< message[recipient]

Where person_detail is a view of person.

This request:

GET "/message?select=*,sender(*)"

Is ambiguous. Both person or person_detail could be embedded.

Until now we have returned the first detected relationship but
now we return a 300 Multiple Choices error with a
descriptive error message asking the user to disambiguate.

This is more helpful for the user and also aids in cases of more
complex relationships.

test/Feature/QueryLimitedSpec.hs

@@ -37,7 +37,7 @@ spec =
         }
 
     it "succeeds in getting parent embeds despite the limit, see #647" $
-      get "/tasks?select=id,project(id)&id=gt.5"
+      get "/tasks?select=id,project:projects(id)&id=gt.5"
         `shouldRespondWith` [json|[{"id":6,"project":{"id":3}},{"id":7,"project":{"id":4}}]|]
         { matchStatus  = 200
         , matchHeaders = ["Content-Range" <:> "0-1/*"]