fix: check whether org exists before creating user (#11647)

# Which Problems Are Solved

It was possible to create a user with an imaginary org.

# How the Problems Are Solved

Check whether org exists before creating the user.

# Additional Changes


# Additional Context

- Closes #11532

internal/api/grpc/user/v2/integration_test/user_test.go

@@ -3452,6 +3452,34 @@ func TestServer_CreateUser(t *testing.T) {
 				}
 			},
 		},
+		{
+			name: "org does not exist human, using IAM owner, error",
+			testCase: func(runId string) testCase {
+				username := fmt.Sprintf("donald.duck+%s", runId)
+				email := username + "@example.com"
+				return testCase{
+					args: args{
+						IamCTX,
+						&user.CreateUserRequest{
+							OrganizationId: "does not exist",
+							Username:       &username,
+							UserType: &user.CreateUserRequest_Human_{
+								Human: &user.CreateUserRequest_Human{
+									Profile: &user.SetHumanProfile{
+										GivenName:  "Donald",
+										FamilyName: "Duck",
+									},
+									Email: &user.SetHumanEmail{
+										Email: email,
+									},
+								},
+							},
+						},
+					},
+					wantErr: true,
+				}
+			},
+		},
 		{
 			name: "org does not exist machine, error",
 			testCase: func(runId string) testCase {
@@ -3473,6 +3501,27 @@ func TestServer_CreateUser(t *testing.T) {
 				}
 			},
 		},
+		{
+			name: "org does not exist machine, using IAM owner, error",
+			testCase: func(runId string) testCase {
+				username := fmt.Sprintf("donald.duck+%s", runId)
+				return testCase{
+					args: args{
+						IamCTX,
+						&user.CreateUserRequest{
+							OrganizationId: "does not exist",
+							Username:       &username,
+							UserType: &user.CreateUserRequest_Machine_{
+								Machine: &user.CreateUserRequest_Machine{
+									Name: integration.Username(),
+								},
+							},
+						},
+					},
+					wantErr: true,
+				}
+			},
+		},
 	}
 	for i, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {