add support for climate action (#720)

* add support for climate action:

Following hass implementation of climate, action represents the current action the climate device is perfoming, e.g. cooling or heating

fix bang_bang climate:

make sure that the thresholds are always respected.
fixes the issue where the component would just keep on heating, regardless of the temperature range

* Updates

- Use dedicated enum for action (otherwise it gets confusing because "auto" is not a valid action)
- Add field to tell HA that action is supported
- Revert semantic changes in bang_bang

* Conditional print


Co-authored-by: Otto Winter <otto@otto-winter.com>

esphome/components/climate/climate_mode.cpp

@@ -17,6 +17,18 @@ const char *climate_mode_to_string(ClimateMode mode) {
       return "UNKNOWN";
   }
 }
+const char *climate_action_to_string(ClimateAction action) {
+  switch (action) {
+    case CLIMATE_ACTION_OFF:
+      return "OFF";
+    case CLIMATE_ACTION_COOLING:
+      return "COOLING";
+    case CLIMATE_ACTION_HEATING:
+      return "HEATING";
+    default:
+      return "UNKNOWN";
+  }
+}
 
 }  // namespace climate
 }  // namespace esphome