Deploy and transactionally in-place with bootable container images.

The `bootc` project currently uses ostree-containers as a backend to support a model of bootable
container images.  Once installed, whether directly via `bootc install` (executed as part of a
container) or via another mechanism such as an OS installer tool, further updates can be pulled and
`bootc upgrade`.

Usage: bootc <COMMAND>

Commands:
  upgrade         Download and queue an updated container image to apply
  switch          Target a new container image reference to boot
  rollback        Change the bootloader entry ordering; the deployment under `rollback` will be
                  queued for the next boot, and the current will become rollback.  If there is a
                  `staged` entry (an unapplied, queued upgrade) then it will be discarded
  edit            Apply full changes to the host specification
  status          Display status
  usr-overlay     Add a transient overlayfs on `/usr`
  install         Install the running container to a target
  container       Operations which can be executed as part of a container build
  loader-entries  Operations on Boot Loader Specification (BLS) entries
  uki-addon       Perform operations related to UKI Addons
  help            Print this message or the help of the given subcommand(s)

Options:
  -h, --help
          Print help (see a summary with '-h')

  -V, --version
          Print version