Adding a custom template for switchable sockets

[PhilJaro]

Is your feature request related to a problem? Please describe.

I would like to add an EVE socket to EVCC. The socket supports Matter, and I have added it to HomeAssistant. Now I can stream the values via MQTT and add it to EVCC, but I can't configure it as a switchable socket.
The configuration breaks because I can't enter the standby power.

Describe the solution you'd like

Add the option to select a custom template for switchable sockets.

Describe alternatives you've considered

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Additional context

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[andig]

Not sure we really need this, but it's also simple to do.