We run osbuild inside of supermin, so for building the live ISO we'll
need all the tools it needs in there. This includes `genisoimage` and
`syslinux-nonlinux`.

We don't currently name `squashfs-tools` as a toplevel dependency. It's
currently pulled in by libguestfs, but we need it in supermin too, so
explicitly list it there.

This adds a new osbuild pipeline for building the live ISO using the new
`org.osbuild.coreos.live-iso` mega stage.

Still missing is changing `cmd-buildextend-live` to call osbuild
instead. I think we'll need to ratchet this in using e.g. an env var
like we did for the other osbuild artifacts. E.g. `COSA_OSBUILD_LIVE`
would control whether to use the old logic or the new one. And then turn
it on in rawhide, etc...

The new `cmd-buildextend-live` would also take care of extracting the
live artifacts from the live ISO to insert into `meta.json`.

…e naming

- Rename `ignition_img_size` to `IGNITION_IMG_SIZE`
and `miniso_data_file_size` to `MINISO_DATA_FILE_SIZE`
for consistent naming convention;
- Move these definitions to the top level for better visibility and maintainability

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>

…creation

- Moved variable declarations and directories creation into generate_iso()
  to enhance clarity and maintainability.

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>

 -  Moved variable declarations to top to enhance clarity.

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>

 - Add support for OSBUILD via COSA_OSBUILD_LIVEISO env var for now.
Once we finish the OSBUILD integration we can disable it via var.

Signed-off-by: Renata Ravanelli <rravanel@redhat.com>