fix(webconfig): pass the build date from the room server too

Adding build_date to the WebConfigServer constructor broke every
*_room_server_observer_mqtt target: simple_room_server constructs the portal as
well, and only simple_repeater was updated. Nothing caught it because every
build run to that point had been a repeater target.

examples/simple_room_server/MyMesh.cpp

@@ -1263,7 +1263,7 @@ bool MyMesh::startWebConfig(bool force_ap, char* reply) {
   }
   if (!_webconfig) {
     _webconfig = new WebConfigServer(&_prefs, _cli.getObserverPrefs(), this,
-                                     self_id.pub_key, getFirmwareVer(), getRole(),
+                                     self_id.pub_key, getFirmwareVer(), getBuildDate(), getRole(),
                                      _cli.getBoard()->getManufacturerName());
   }
   if (force_ap) {