add dualtor fixture for test_dhcp_relay_stress (#16171)

What is the motivation for this PR?
To ensure proper Dual ToR setups in test_dhcp_relay_stress testcase.

How did you do it?
Added the Dual ToR-related fixture.

How did you verify/test it?
Validated that Dual ToR setups successfully pass the test_dhcp_relay_stress test case.

tests/dhcp_relay/test_dhcp_relay_stress.py

@@ -131,8 +131,10 @@ def check_dhcp_stress_status(duthost, test_duration_seconds):
 
 
 @pytest.mark.parametrize('dhcp_type', ['discover', 'offer', 'request', 'ack'])
-def test_dhcp_relay_stress(ptfhost, ptfadapter, dut_dhcp_relay_data, validate_dut_routes_exist,
-                           testing_config, dhcp_type, clean_processes_after_stress_test):
+def test_dhcp_relay_stress(ptfhost, ptfadapter, dut_dhcp_relay_data, validate_dut_routes_exist, testing_config,
+                           setup_standby_ports_on_rand_unselected_tor,
+                           toggle_all_simulator_ports_to_rand_selected_tor_m,     # noqa F811
+                           dhcp_type, clean_processes_after_stress_test):
     """Test DHCP relay functionality on T0 topology
        and verify that HCP relay service can handle the maximum load without failure.
     """