Simplify 'image add' mechanism

Target component

• CLI
• SDK
• Something else
• Not sure

Overview

A CLI user should be able to upload an image file "directly" as an image, the same way a Console user can.

Today the console does the work behind the scenes to do the creation of a temp disk, bulk writes of the image to that temp tdisk, taking the disk out of import mode, creating a temp snapshot of the disk, creating an image from the snapshot, then deleting the temp disk and temp snapshot... all of which makes the image upload process effectively transparent to the user.

It would seem the CLI doesn't have this user-friendly abstraction. What is available doesn't quite give the same nice experience:

• oxide image create: expects a json body and has no docs for what should be in it
• oxide disk import: convoluted (must first be run w/ arguments but w/o a command, then must be run with commands later?) and results in a disk that still needs to be snapshotted and have an image created from it, then cleaned up

Implementation details

No response

Anything else you would like to add?

No response

Start by examining the CLI entry points for oxide image create and oxide disk import, then compare their documented arguments and command flow with the Console behavior described in the issue. Define the direct image-upload workflow and its cleanup steps before implementation; done means a CLI user can upload an image without manually creating and snapshotting a temporary disk.