Feat(GraphQL): This PR allow multiple @id fields in a type. (#7235)

Fixes GRAPHQL-924
Currently, we only allow single xid or external id fields in a type with the @id directive.
Now, we are extending this to have multiple external @id fields in a type. Every such field will be unique over all the nodes of that type. As of now, fields with @id directive will be immutable. get query will work for all the fields with the @id type.
RFC:https://discuss.dgraph.io/t/wip-rfc-allow-multiple-unique-fields-in-graphql-schema/12008
Co-authored-by: Rajas Vanjape <rajas@dgraph.io>

ee/acl/acl_test.go

@@ -233,7 +233,7 @@ func TestCreateAndDeleteUsers(t *testing.T) {
 	resp := createUser(t, token, userid, userpassword)
 	require.Equal(t, 1, len(resp.Errors))
 	require.Equal(t, "couldn't rewrite mutation addUser because failed to rewrite mutation payload because id"+
-		" alice already exists for type User", resp.Errors[0].Message)
+		" alice already exists for field name inside type User", resp.Errors[0].Message)
 	checkUserCount(t, resp.Data, 0)
 
 	// delete the user

graphql/e2e/auth/add_mutation_test.go

@@ -1035,7 +1035,7 @@ func TestUpsertMutationsWithRBAC(t *testing.T) {
 				require.Error(t, gqlResponse.Errors)
 				require.Equal(t, len(gqlResponse.Errors), 1)
 				require.Contains(t, gqlResponse.Errors[0].Error(),
-					"GraphQL debug: id already exists for type Tweets")
+					"GraphQL debug: id tweet1 already exists for field id inside type Tweets")
 			} else {
 				common.RequireNoGQLErrors(t, gqlResponse)
 				require.JSONEq(t, tcase.result, string(gqlResponse.Data))

graphql/e2e/auth/auth_test.go

@@ -351,7 +351,7 @@ func TestAddMutationWithXid(t *testing.T) {
 	require.Error(t, gqlResponse.Errors)
 	require.Equal(t, len(gqlResponse.Errors), 1)
 	require.Contains(t, gqlResponse.Errors[0].Error(),
-		"GraphQL debug: id already exists for type Tweets")
+		"GraphQL debug: id tweet1 already exists for field id inside type Tweets")
 
 	// Clear the tweet.
 	tweet.DeleteByID(t, user, metaInfo)

graphql/e2e/common/common.go

@@ -889,6 +889,7 @@ func RunAll(t *testing.T) {
 	t.Run("cyclically linked mutation", cyclicMutation)
 	t.Run("parallel mutations", parallelMutations)
 	t.Run("input coercion to list", inputCoerciontoList)
+	t.Run("multiple external Id's tests", multipleXidsTests)
 	t.Run("Upsert Mutation Tests", upsertMutationTests)
 
 	// error tests