Add Entity categories for Home Assistant (#2636)

esphome/components/wifi_signal/sensor.py

@@ -4,6 +4,7 @@ from esphome.components import sensor
 from esphome.const import (
     CONF_ID,
     DEVICE_CLASS_SIGNAL_STRENGTH,
+    ENTITY_CATEGORY_DIAGNOSTIC,
     STATE_CLASS_MEASUREMENT,
     UNIT_DECIBEL_MILLIWATT,
 )
@@ -20,6 +21,7 @@ CONFIG_SCHEMA = (
         accuracy_decimals=0,
         device_class=DEVICE_CLASS_SIGNAL_STRENGTH,
         state_class=STATE_CLASS_MEASUREMENT,
+        entity_category=ENTITY_CATEGORY_DIAGNOSTIC,
     )
     .extend(
         {