file-restore-daemon: add binary with virtio-vsock API server

file-restore-daemon: add binary with virtio-vsock API server

Implements the base of a small daemon to run within a file-restore VM.

The binary spawns an API server on a virtio-vsock socket, listening for
connections from the host. This happens mostly manually via the standard
Unix socket API, since tokio/hyper do not have support for vsock built
in. Once we have the accept'ed file descriptor, we can create a
UnixStream and use our tower service implementation for that.

The binary is deliberately not installed in the usual $PATH location,
since it shouldn't be executed on the host by a user anyway.

For now, only the API calls 'status' and 'stop' are implemented, to
demonstrate and test proxmox::api functionality.

Authorization is provided via a custom ApiAuth only checking a header
value against a static /ticket file.

Since the REST server implementation uses the log!() macro, we can
redirect its output to stdout by registering env_logger as the logging
target. env_logger is already in our dependency tree via zstd/bindgen.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>