Allow changing standby image

[Julusian]

As of the v4.9.0 of the elgato software it is possible to change the 'screensaver'.
This needs proper reverse engineering and exposing in the api

[Phygon]

Is this "update boot logo" in the docs?

https://docs.elgato.com/streamdeck/hid/module-15_32#update-boot-logo