Add support for discovery device trigger

[Odyno]

In short

• Add support for MQTT Device Trigger.
• Add Example on Documentation
• Used on RF Discovery

More

The MQTT Device Trigger platform uses an MQTT message payload to generate device trigger events in to home assistant, so it's not create a flag/state/etc on the device (like what produced by binary sensor) but just declare where the event will be raise and provide information about the event.

I used this feature in the auto discovery process for the RF module, so we can reactivate what has been deactivated here this PR #1026

It will also solve the problem #939 because the Device Trigger already has all the reset and event management logic, which by definition has no state.

Checklist:

• The pull request is done against the latest development branch
• Only one feature/fix was added per PR and the code change compiles without warnings
• I accept the DCO.

[1technophile]

Thanks for the PR,

I used this feature in the auto-discovery process for the RF module, so we can reactivate what has been deactivated here this PR #1026

The auto-discovery process of RF has been deactivated because it was creating a lot of unnecessary entities into Home Assistant, in particular when there is a lot of RF devices in the neighborhood. Does this new method prevent this?

[Odyno]

If I understand what you mean, yes I confirm that no entities appear, this is my configuration: I have 3 gateways made with the az-delivery esp32 board each one with SRX882 and STX882. In my house there are about 30 RF devices and a lot of Bluetooth devices... that's my current board on HA:

To date I have intercepted over 350 RF signals and have none of these entities

[1technophile]

To explain better, let's suppose that a device that doesn't belong to you emit a set of RF signals, 1145896, 1458765, 3555489.
This is the weather station of your neighbor. Do you think this is going to create one entity for each signal?

[Odyno]

Confirmed, no entity for each signal. In HA it is part of the triggers, more specifically the device trigger

[Odyno]

🥳 Time to review the code and I provider you the pr as promised!