Make model listing faster

[nlathia]

another nice to have -> some performance (latency) improvements around methods like list_models i haven't had the chance to take an in depth look but at first guess, probably adding async / multithreading for the IO blocking parts or using ujson instead of json for loading the jsons?

https://mlops-community.slack.com/archives/C0227QJCDS8/p1687856991359489?thread_ts=1687777412.934619&cid=C0227QJCDS8