Add state_class total (#3608)

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

esphome/components/sensor/sensor.cpp

@@ -12,6 +12,8 @@ std::string state_class_to_string(StateClass state_class) {
       return "measurement";
     case STATE_CLASS_TOTAL_INCREASING:
       return "total_increasing";
+    case STATE_CLASS_TOTAL:
+      return "total";
     case STATE_CLASS_NONE:
     default:
       return "";