Add support for "mqtt" actions

[sumnerboy12]

Similar to "http", allow a notification action to send an MQTT message.

MQTT is a very common protocol for home automation. Having the ability to send an MQTT message from a ntfy notification action would allow all sorts of integrations.

I will also be looking to add support for ntfy to mqttwarn. This would allow for users to send notifications to an MQTT topic and mqttwarn will automatically forward it to ntfy.

With MQTT actions and mqttwarn integration, we would have bi-directional support for MQTT based systems.

[binwiederhier]

Related: #8

[jpmens]

MQTT support in ntfy would be grand.

@sumnerboy12 I've added an enhancement issue to mqttwarn here, so if you've nothing better to do ... :-)

[zoic21]

Hello,
I think it's can be a awesome idea. MQTT is more and more used especially by iot, place where ntfy.sh is used a lot. With mqtt (api and action) we can used ntfy.sh to send message from ESP32 (it's possible in HTTP but the library is very heavy compared to MQTT, when there is only 4mb or even 1mb it is not negligible). And with the actions from the notification, you can imagine direct control scenarios without necessarily needing a home automation solution in the middle.

One can imagine when I open my garage door the module sends an MQTT frame to ask if I also need to open the gates. If I answer yes the portal module sees the request and executes

I don't see the work that it represents, especially in go, a language that I don't know, but on the other hand I can see the opening it gives in the home automation environment.

[osering]

MQTT (opensource standard as well) bridge/integration would be invaluable. It'll let connect thousands of ESP8266 boards (including with TASMOTA/ESPurna/ESPeasy/ESPhome firmware and MQTT) with ntfy gateway! Most of Sonoff gear and many of the Tuya gear can be Tasmotized!
Probably united ntfy/mqtt server/broker could be crafted...
Some relevant links:
https://github.com/arendst/Tasmota
https://templates.blakadder.com/howto.html
https://www.emqx.io/
https://github.com/eclipse/mosquitto