Add API connection status sensor (#774)

As requested by users:
- https://github.com/Blackymas/NSPanel_HA_Blueprint/discussions/735#discussioncomment-5755419

Could this be used to prevent some of the "Loading..." or perhaps update screen when connection is reestablished?

nspanel_esphome.yaml

@@ -557,6 +557,10 @@ binary_sensor:
     entity_category: diagnostic
     icon: mdi:tablet-dashboard
 
+  ##### API connection status
+  - platform: status
+    name: ${device_name} Status
+
 ##### START - SENSOR CONFIGURATION #####
 sensor: