feat: add service name to app-server (#12319)

Add service name to the app-server so that the app can use it's own
service name

This is on thread level because later we might plan the app-server to
become a singleton on the computer

codex-rs/app-server-protocol/src/protocol/v2.rs

@@ -1661,6 +1661,8 @@ pub struct ThreadStartParams {
     #[ts(optional = nullable)]
     pub config: Option<HashMap<String, JsonValue>>,
     #[ts(optional = nullable)]
+    pub service_name: Option<String>,
+    #[ts(optional = nullable)]
     pub base_instructions: Option<String>,
     #[ts(optional = nullable)]
     pub developer_instructions: Option<String>,