Fix cast.show_lovelace_view service description (#140859)

homeassistant/components/cast/services.yaml

@@ -7,11 +7,11 @@ show_lovelace_view:
           integration: cast
           domain: media_player
     dashboard_path:
-      required: true
       example: lovelace-cast
       selector:
         text:
     view_path:
+      required: true
       example: downstairs
       selector:
         text:

homeassistant/components/cast/strings.json

@@ -49,7 +49,7 @@
         },
         "dashboard_path": {
           "name": "Dashboard path",
-          "description": "The URL path of the dashboard to show."
+          "description": "The URL path of the dashboard to show, defaults to lovelace if not specified."
         },
         "view_path": {
           "name": "View path",