Explicitly include "Alexa" Interface in discovery response (#28218)

* Explicitly include Alexa Interface to discovery response.

* Updated cloud component test to reflect additional Alexa interface.

* Updated test for recently added SeekController.

tests/components/cloud/test_http_api.py

@@ -801,7 +801,7 @@ async def test_list_alexa_entities(hass, hass_ws_client, setup_api, mock_cloud_l
     assert response["result"][0] == {
         "entity_id": "light.kitchen",
         "display_categories": ["LIGHT"],
-        "interfaces": ["Alexa.PowerController", "Alexa.EndpointHealth"],
+        "interfaces": ["Alexa.PowerController", "Alexa.EndpointHealth", "Alexa"],
     }