Draft the leaderboard functionality

[TheEimer]

Needs a layout, a way to store and submit data and should be accessible easily.

[TheEimer]

This is finally done and ready for feedback! Here's the link: https://huggingface.co/spaces/autorl-org/arlbench-leaderboard

Currently this is demo data for one algorithm only, but refreshing/filtering works. Submission works like this: you add a file via PR to this dataset https://huggingface.co/datasets/autorl-org/arlbench-leaderboard-results/tree/main and then it shows up in the leaderboard.