add registerTime in ApplicationInstanceMapping because of the register recover...

add registerTime in ApplicationInstanceMapping because of the register recover service need the origin register time

apm-network/src/main/proto/DiscoveryService.proto

@@ -26,6 +26,7 @@ message ApplicationInstance {
 message ApplicationInstanceMapping {
     int32 applicationId = 1;
     int32 applicationInstanceId = 2;
+    int64 registerTime = 3;
 }
 
 message ApplicationInstanceHeartbeat {