Only log message about starting extensions in debug mode

jupyter_server/extension/manager.py

@@ -416,7 +416,7 @@ async def start_extension(self, name):
                     "%s | extension failed starting with message: %r", name, e, exc_info=True
                 )
             else:
-                self.log.info("%s | extension was successfully started.", name)
+                self.log.debug("%s | extension was successfully started.", name)
 
     async def stop_extension(self, name, apps):
         """Call the shutdown hooks in the specified apps."""