Allow instance of Device to override Front and Rear Image stored in DeviceType

[Ximalas]

For a chassis switch it would be better to display an image of the specific device instance in rack views instead of displaying the image stored for the device type, which is typically an empty chassis. I know we can add additional images for the specific device instances, but none of these can be marked as preferred when displaying rack elevations.

[Ximalas]

This idea is being pursued in #19032