Handle the naming of the (HF_)TOKEN variable
Demo leaderboard & backend had sometimes had TOKEN, sometimes HF_TOKEN as the relevant variable name. We standardized to TOKEN, but creating an inference endpoint via the demo leaderboard won't work because this lighteval code (which the demo leaderboard calls to) expects the variable to be named HF_TOKEN. Here I propose a solution that will adapt to the TOKEN name, but not break any other dependencies that assume HF_TOKEN.
