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/api/api.proto

@@ -644,6 +644,12 @@ enum ClimateMode {
   CLIMATE_MODE_COOL = 2;
   CLIMATE_MODE_HEAT = 3;
 }
+enum ClimateAction {
+  CLIMATE_ACTION_OFF = 0;
+  // values same as mode for readability
+  CLIMATE_ACTION_COOLING = 2;
+  CLIMATE_ACTION_HEATING = 3;
+}
 message ListEntitiesClimateResponse {
   option (id) = 46;
   option (source) = SOURCE_SERVER;
@@ -661,6 +667,7 @@ message ListEntitiesClimateResponse {
   float visual_max_temperature = 9;
   float visual_temperature_step = 10;
   bool supports_away = 11;
+  bool supports_action = 12;
 }
 message ClimateStateResponse {
   option (id) = 47;
@@ -675,6 +682,7 @@ message ClimateStateResponse {
   float target_temperature_low = 5;
   float target_temperature_high = 6;
   bool away = 7;
+  ClimateAction action = 8;
 }
 message ClimateCommandRequest {
   option (id) = 48;