Allow to add a wallpaper background to screenshots

[AvdLee]

Configuring padding and a background image, resulting in something like:

See: https://twitter.com/anikaseibezeder/status/1629581776812232705/photo/1

[ohwhen]

@AvdLee I would love to have this feature, currently there is no easy tool that does this! Most tooling only support static images, no video, this would be huge.