vmm: dbus: implement the D-Bus API

This commit introduces three new dependencies: `zbus`, `futures`
and `blocking`. `blocking` is used to call the Internal API in zbus'
async context which is driven by `futures::executor`. They are all
behind the `dbus_api` feature flag.

The D-Bus API implementation is behind the same `dbus_api` feature
flag as well.

Signed-off-by: Omer Faruk Bayram <omer.faruk@sartura.hr>

Cargo.toml

@@ -65,6 +65,7 @@ wait-timeout = "0.2.0"
 
 [features]
 default = ["kvm"]
+dbus_api = ["vmm/dbus_api"]
 dhat-heap = ["dhat"] # For heap profiling
 guest_debug = ["vmm/guest_debug"]
 kvm = ["vmm/kvm"]