install: logically bound images are not installed with --composefs-backend #2540

With --composefs-backend, bootc install doesn't copy logically bound images into the installed system. The install exits 0 and prints nothing about bound images. The same install without --composefs-backend puts the image in /ostree/bootc/storage.

Reproduced on quay.io/fedora/fedora-bootc:44 (bootc 1.16.13), binding a busybox image by a tag that is in the host storage before the install:

podman pull docker.io/library/busybox@sha256:f97baa533a26513c453a362be331a43eb60214302f449c16571b23cea141dce4
podman tag docker.io/library/busybox@sha256:f97baa533a26513c453a362be331a43eb60214302f449c16571b23cea141dce4 docker.io/library/busybox:latest

FROM quay.io/fedora/fedora-bootc:44@sha256:5ab8ee5189bb0f3870279723f5343474df002d8d6f46564702b3ad3ba7382d98
COPY bound.container /usr/share/containers/systemd/bound.container
RUN mkdir -p /usr/lib/bootc/bound-images.d && ln -s /usr/share/containers/systemd/bound.container /usr/lib/bootc/bound-images.d/bound.container

# bound.container
[Container]
Image=docker.io/library/busybox:latest

podman build -t localhost/gaprepro:1 .
truncate -s 20G a.raw b.raw
podman run --rm --privileged --pid=host --security-opt label=type:unconfined_t \
  -v /dev:/dev -v /var/lib/containers:/var/lib/containers -v $PWD:/out localhost/gaprepro:1 \
  bootc install to-disk --via-loopback --filesystem ext4 --generic-image --wipe \
  --composefs-backend /out/a.raw
# the same again without --composefs-backend, writing b.raw

With each root partition mounted, ostree/bootc/storage/overlay-images/images.json on the ostree disk lists busybox:latest. The composefs disk has no container storage, and the only file on it that mentions busybox is the stock 000-shortnames.conf.

The composefs install doesn't read bound-images.d at all. With a regular file there instead of a symlink, the ostree install fails with Querying bound images: Not a symlink: bound.container, and the composefs install completes.

BoundImages::from_state is called only from ostree_install (install.rs L2092), and the copy happens in install_with_sysroot (L2029-L2043). The composefs branch (L2156-L2226) has neither, and plan-22-logically-bound-install is skipped on composefs (integration.fmf L69-L75).

I'd expect bound images to be present at first boot on both backends, as bootc-logically-bound-images(7) describes.

Related: #2290, which pulls bound images on the composefs deploy path.