Add support for Sensor state class (#1835)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/max6675/sensor.py

@@ -1,7 +1,13 @@
 import esphome.codegen as cg
 import esphome.config_validation as cv
 from esphome.components import sensor, spi
-from esphome.const import CONF_ID, DEVICE_CLASS_TEMPERATURE, ICON_EMPTY, UNIT_CELSIUS
+from esphome.const import (
+    CONF_ID,
+    DEVICE_CLASS_TEMPERATURE,
+    ICON_EMPTY,
+    STATE_CLASS_MEASUREMENT,
+    UNIT_CELSIUS,
+)
 
 max6675_ns = cg.esphome_ns.namespace("max6675")
 MAX6675Sensor = max6675_ns.class_(
@@ -9,7 +15,9 @@ MAX6675Sensor = max6675_ns.class_(
 )
 
 CONFIG_SCHEMA = (
-    sensor.sensor_schema(UNIT_CELSIUS, ICON_EMPTY, 1, DEVICE_CLASS_TEMPERATURE)
+    sensor.sensor_schema(
+        UNIT_CELSIUS, ICON_EMPTY, 1, DEVICE_CLASS_TEMPERATURE, STATE_CLASS_MEASUREMENT
+    )
     .extend(
         {
             cv.GenerateID(): cv.declare_id(MAX6675Sensor),