Move MQTT discovery hass.data globals to dataclass (#78706)

* Add MQTT discovery hass.data globals to dataclass

* isort

* Additional rework

* Add hass.data["mqtt_tags"] to dataclass

* Follow-up comment

* Corrections

tests/components/mqtt/test_config_flow.py

@@ -186,7 +186,18 @@ async def test_manual_config_set(
         "discovery": True,
     }
     # Check we tried the connection, with precedence for config entry settings
-    mock_try_connection.assert_called_once_with(hass, "127.0.0.1", 1883, None, None)
+    mock_try_connection.assert_called_once_with(
+        {
+            "broker": "bla",
+            "keepalive": 60,
+            "discovery_prefix": "homeassistant",
+            "protocol": "3.1.1",
+        },
+        "127.0.0.1",
+        1883,
+        None,
+        None,
+    )
     # Check config entry got setup
     assert len(mock_finish_setup.mock_calls) == 1
     config_entry = hass.config_entries.async_entries(mqtt.DOMAIN)[0]