feat: add persistence for last deployment path in Nginx handler

crates/nxmesh-proto/proto/agent.proto

@@ -68,8 +68,9 @@ message ConfigContent {
 
 message ConfigUpdateResult {
   string config_id = 1; // should match the config_id in ConfigUpdate
-  bool success = 2;
-  ConfigUpdateError error_message = 3; // if success is false, this field should contain the error message
+  string version = 2;
+  bool success = 3;
+  optional ConfigUpdateError error_message = 4; // if success is false, this field should contain the error message
 }
 
 enum ConfigUpdateError {
@@ -83,6 +84,8 @@ enum ConfigUpdateError {
 //
 //
 
+// TODO: allow setting the default fallback and the corresponding default nginx root config when nginx reload fails to re-use old config, "use default config", "stop nginx".
+
 // Command represents a request from master to agent to execute a command, e.g. "reload", "test"
 message Command {
   oneof command {