`from-image`: can't specify silo image by name

The code assumes that an image specified by name is a project image.

https://github.com/oxidecomputer/oxide.rs/blob/77a04019aa1ac794b28b2bfa158eb318b2d5a0fc/cli/src/cmd_instance.rs#L247-L251

I see two ways around this, neither great. I think I prefer the second.

• Add a way of indicating when you want a silo image by name
  • Instead of --image maybe have mutually exclusive --project-image and --silo-image flags?
  • I considered --image + --image-project but a) that project will always be the same as the --project project when specified, b) confusing name
• Avoid the problem by only allowing specifying an image by ID, which is pretty easily conveyed by the help text and the argument name. You could call it --image-id, that would be pretty unambiguous. That requires the user to use oxide image view view get the ID first.

Of course, by taking out half of what this command does for you, option 2 pushes us more in the direction of getting rid of it altogether.

Yeah... I'm even more of the opinion that hand-rolled subcommands such as this one may be a step in the wrong direction.

https://github.com/oxidecomputer/oxide.rs/issues/373#issuecomment-1734554026

Start with cli/src/cmd_instance.rs lines 247-251 and the linked discussion in issue #373. Compare the proposed handling for project and silo image names with the alternative of accepting only an image ID. Done requires an agreed command interface and behavior for selecting or identifying silo images.