agent: add signal value to log

For signal_process call, log the signal value in logs.

Signed-off-by: Bin Liu <bin@hyper.sh>

src/agent/src/rpc.rs

@@ -382,6 +382,7 @@ impl AgentService {
             "signal process";
             "container-id" => cid.clone(),
             "exec-id" => eid.clone(),
+            "signal" => req.signal,
         );
 
         let mut sig: libc::c_int = req.signal as libc::c_int;