[feat] Add support for Home Assistant event entities

[mundschenk-at]

Adds support for Home Assistant's new-ish event entities. Fixes #18389.

[Koenkk]

This looks like an alternative to MQTT device trigger. It's a bit unclear what exactly the pros/cons are.

I think this also deserves some docs here.

[mundschenk-at]

I think at this point device triggers are somewhat deprecated (not officially, but the event entity is easier to work with when writing automations for multiple devices). With device triggers, when you change the underlying device, you can't reuse the triggers because the all have unique IDs, where as with an event entity you just need to change entity name (as long as the events are the same for the new device).

[thecode]

This looks like an alternative to MQTT device trigger. It's a bit unclear what exactly the pros/cons are.

Historically HA team did not agree creating entities for things that are momentary (mostly push buttons style) since they create multiple events and there was an intention to reduce the number of states stored in the DB (so you mostly don't want to store push and release of each button), since device triggers was complicated and not intuitive for most users and storing states became more efficient HA team created the event entities.

Event entities are more trivial to understand, they are similar to other entities, they hold the time and event of the last event while device triggers are completely out of the state machine.

What I wrote above does not eliminate the need to document the new feature 😸

[mundschenk-at]

I think this also deserves some docs here.

I have added a documentation PR: Koenkk/zigbee2mqtt.io#3112

[Koenkk]

Thanks!