Adding AHT21 Temp Humidity Sensor

Added the AHT21 Temperature/ Humidity Sensor

Author: thussaiththelaw

components/i2c/AHT21/definition.json

@@ -0,0 +1,5 @@
+{
+    "displayName": "aht21",
+    "i2cAddresses": [ "0x38"],
+    "subcomponents": [ "ambient-temp", "ambient-temp-fahrenheit" ]
+}