Request: add nextcloudpi to raspberry pi imager

[dhombios]

Description

Raspberry pi imager already provides images of other third party operating systems and adding nextcloudpi would simplify installing it. This can be achieved by opening an issue in https://github.com/raspberrypi/rpi-imager with a json with the required links (see https://github.com/raspberrypi/rpi-imager/issues/162 )

Example

OctoPi json can be used as a reference:

{
    "os_list": [
        {
            "name": "OctoPi",
            "description": "A Raspberry Pi distribution for 3d printers. Ships OctoPrint out-of-the-box.",
            "icon": "https://raw.githubusercontent.com/guysoft/OctoPi/devel/media/rpi-imager-OctoPi.png",
            "subitems_url": "http://unofficialpi.org/rpi-imager/rpi-imager-octopi.json"
        }
    ]
}

Aditionally, icon needs to be provided as a 40x40 image