Label emergency heat switch (#139872)

* Add label to emergency heat switch

* Use sentence case names

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

---------

Co-authored-by: Franck Nijhof <frenck@frenck.nl>

homeassistant/components/nexia/strings.json

@@ -58,6 +58,9 @@
     "switch": {
       "hold": {
         "name": "Hold"
+      },
+      "emergency_heat": {
+        "name": "Emergency heat"
       }
     }
   },