feat: add one to one relationship for embedding

BREAKING CHANGE: For the cases where one to one relationships are
detected, json objects will be returned instead of json arrays of length
1.

If you wish to override this behavior, you can use computed
relationships to return arrays again.

test/spec/Feature/Query/EmbedDisambiguationSpec.hs

@@ -106,6 +106,20 @@ spec =
           , matchHeaders = [matchContentTypeJson]
           }
 
+      it "errs on an ambiguous embed that has two one-to-one relationships" $
+        get "/first?select=second(*)" `shouldRespondWith`
+          [json| {
+            "code":"PGRST201",
+            "details":[
+              {"cardinality":"one-to-one","embedding":"first with second","relationship":"first_second_id_1_fkey using first(second_id_1) and second(id)"},
+              {"cardinality":"one-to-one","embedding":"first with second","relationship":"first_second_id_2_fkey using first(second_id_2) and second(id)"}
+            ],
+            "hint":"Try changing 'second' to one of the following: 'second!first_second_id_1_fkey', 'second!first_second_id_2_fkey'. Find the desired relationship in the 'details' key.","message":"Could not embed because more than one relationship was found for 'first' and 'second'"
+            }|]
+          { matchStatus  = 300
+          , matchHeaders = [matchContentTypeJson]
+          }
+
     context "disambiguating requests with embed hints" $ do
 
       context "using FK to specify the relationship" $ do