Support uncompressed images

[atanasdinov]

Users can easily assume that they can feed EIB an uncompressed image (right after downloading it). This will now fail with a non-obvious error:

shardy@localhost:~/metal3-demo-files/eib/_build/build-Jan10_14-46-38> cat raw-build.log
guestfish: no operating system was found on this disk

If using guestfish ‘-i’ option, remove this option and instead
use the commands ‘run’ followed by ‘list-filesystems’.
You can then mount filesystems you want by hand using the
‘mount’ or ‘mount-ro’ command.

If using guestmount ‘-i’, remove this option and choose the
filesystem(s) you want to see by manually adding ‘-m’ option(s).
Use ‘virt-filesystems’ to see what filesystems are available.

If using other virt tools, this disk image won’t work
with these tools.  Use the guestfish equivalent commands
(see the virt tool manual page).
shardy@localhost:~/metal3-demo-files/eib/_build/build-Jan10_14-46-38> cat eib-build.log
2024-01-10T14:46:38.438Z	INFO	combustion/network.go:50	Configuring network component...
2024-01-10T14:46:38.439Z	INFO	combustion/network.go:54	Skipping network component, configuration is not provided
2024-01-10T14:46:38.439Z	INFO	combustion/elemental.go:30	Skipping elemental registration component, configuration is not provided
2024-01-10T14:46:50.521Z	FATAL	eib/main.go:126	An error occurred building the image: running the image modification script: exit status 1
main.main
	/src/cmd/eib/main.go:126
runtime.main
	/usr/lib64/go/1.21/src/runtime/proc.go:267

We should either:

• Enforce validation for the file type
• Add support for uncompressing the input image if necessary

[jdob]

For 1.0 (Edge 3.0), this will be covered in documentation. Aligned to that release so we make sure we do it, then we'll create a follow up issue to track a code implementation of this.