sysroot: Stabilize deployment finalization, add API and CLI

sysroot: Stabilize deployment finalization, add API and CLI

It's about time we do this; deployment finalization locking
is a useful feature.  An absolutely key thing here is that
we've slowly been moving towards the deployments as the primary
"source of truth".

Specifically in bootc for example, we will GC container images
not referenced by a deployment.

This is then neecessary to support a "pull but don't apply automatically" model.

This stabilizes the existing `ostree admin deploy --lock-finalization`
CLI, and adds a new `ostree admin unlock-finalization`.

We still check the old lock file path, but there's a new boolean
value as part of the staged deployment data which is intended
to be the source of truth in the future.  At some point then we
can drop the rpm-ostree lockfile handling.

Closes: https://github.com/ostreedev/ostree/issues/3025