One possibility would be a Shelly Button with a Shelly 1 inside.
It can use its own firmware or be flashed by something like ESPHome (both are supported in Home Assistant)
The setup is not cheap, though (~12€ piece)
That diagram is describing Google Assistant's Local Control SDK.
2 Resistors and then anything with a 3.3v GPIO input pin (e.g. ESP8266)
You need to build a voltage divider, the equations (or this calculator) on that page will help you work out what the ratio of the 2 resistor values need to be (But something like 20 kohm and 7.5 kohm should be in the right ball park).
When the pin goes high, you can then make a HTTP ...