Cache /valid?
<strike>It is called multiple times per second by moon landing, and it impacts a lot the loading time of the /datasets page (https://github.com/huggingface/moon-landing/issues/1871#issuecomment-1024414854).</strike>

Currently, several queries are done to check all the valid datasets on every request
Cache /valid?: <strike>It is called multiple times per second by moon landing, and it impacts a lot the loading time of the /datasets page (https://github.com/huggingface/moon-landing/issues/1871#issuecomment-1024414854).</strike>

Currently, several queries are done to check all the valid datasets on every request