[BUG] - `instance iso` offers no way to detach ISO from instance

[RobertKosten]

Describe the bug
The documentation clearly states that the command allows detaching of the ISO from an instance:

The vultr-cli instance iso command manages ISO attachments for Vultr instances, allowing users to attach, detach, and view ISO images on their virtual machines.

Yet only attach and status are available as sub-commands. attach also requires a valid iso uuid, so no workarounds like ``,null, `nil`, or `00000000-0000-0000-0000-000000000000` seem possible, making detachment of ISOs something that can only be done manually via the GUI or direct API call.