[FEAT]: Keep track of token usage per user

[erickrf]

What would you like to see?

As an instance admin, it would be great to be able to see the token usage per user (and possibly per workspace as well).

This metric must already be tracked internally, in order for the limit of tokens per user per day to work, but as far as I could tell, it is nowhere visible in the UI (the Onboard AI chatbot confirms this).

This is particular useful in corporate settings as we analyze patterns of LLM usage.