Images with uuid_validity: none can't be deleted via --delete

[Lappihuan]

For example Gardenlinux Images can't be auto deleted via --delete:

Image 'Garden Linux 1592.8' will not be deleted, UUID validity is 'none'

It seems like this feature would only work with "multi" images for now but could make a lot of sense for Gardenlinux:

openstack-image-manager/openstack_image_manager/main.py

Lines 1036 to 1044 in 4d2b1b1

	if self.CONF.keep and not image_definition["multi"]:
	logger.info(
	f"Image '{image}' will not be deleted, undefined versions of defined images are kept"
	)
	elif uuid_validity == "none":
	logger.info(
	f"Image '{image}' will not be deleted, UUID validity is 'none'"
	)

I'm unsure how this should behave ideally so it does not delete images for other users.