Support custom mqtt state_on/state_off and payload_on/payload_off

**Describe the problem you have/What new integration you would like**

Some systems use custom mqtt conventions. For example [homeA mqtt](https://github.com/binarybucks/homA/wiki/Conventions) convention use payload_on=1 (instead of "On") and payload_off=0(instead of "Off")

**Please describe your use case for this integration and alternatives you've tried:**

In home-assistant it is possible to support such convention with next setup:
- platform: mqtt
name: Kitchen
state_topic: /devices/thermostat/controls/kitchen_enabled
command_topic: /devices/thermostat/controls/kitchen_enabled/on
_payload_on: 1
payload_off: 0
state_on: 1
state_off: 0_
icon: mdi:radiator

**Additional context**

Can't find any possibility to support such mqtt convention natively in Esphome.