vmm: Report enabled features from the '/vmm.ping' endpoint

Fixes: #5817

Signed-off-by: Bo Chen <chen.bo@intel.com>

vmm/src/api/mod.rs

@@ -171,6 +171,7 @@ pub struct VmmPingResponse {
     pub build_version: String,
     pub version: String,
     pub pid: i64,
+    pub features: Vec<String>,
 }
 
 #[derive(Clone, Deserialize, Serialize, Default, Debug)]