Comment 4 for bug 1830301

I think there should be some built-in support for these new read-only properties, perhaps even showing read-only form fields that don't get posted when updating the custom image properties. However, this is a bigger change.

I've added back an implementation of IMAGE_RESERVED_CUSTOM_PROPERTIES, and tested that the Image Custom Properties form now works in Rocky with this setting:

IMAGE_RESERVED_CUSTOM_PROPERTIES = ['os_hash_algo', 'os_hash_value']

This should buy some time for a proper solution to be worked on. It also re-enables the documented setting in case anybody has need of the underlying functionality for their own custom properties.

Please review, and then we should backport to Stein and Rocky. I am testing with Rocky.