Add openHAB in Raspberry Imager

[Larsen-Locke]

openHAB is currently not selectable as an image in the Raspberry Imager. This PR corrects this shortcoming. For this, Raspberry Imager needs a json file on the download location of the image that contains the path to the current image and checksums. The json is generated from a template in build.bash and made available via the build workflow. As soon as the json file is online, I would raise the corresponding issue at rpi-imager (analogue https://github.com/raspberrypi/rpi-imager/issues/427). The PR solves my issue: https://github.com/openhab/openhabian/issues/1703 The option will look like this in the Raspberry Imager: