Options for wled power off

[falo2k]

Is your feature request related to a problem? Please describe

While we can initialise wled state from moonraker, and subsequently control it through gcode, we can't then turn the wled instance off when the printer or host powers down.

Describe the solution you'd like

It would be nice to have the option to link it to a [power] device so that it will turn lighting off when power is toggled. Either just a boolean flag, or be able to provide a specific power section name to link it to. It would also be helpful if the wled state could be turned off with a system shutdown / moonraker service shutdown.

Describe alternatives you've considered

Using external monitoring (e.g. Home Assistant) to power down the wled LEDs when it detects the printer is off or inaccessible on the network.

Additional information

May be some crossover with #856 (on the state when shutdown front) and could be implemented through #860 as a workaround for the power off trigger.