token counter

[roworu]

need to implement following:

1. save token usage to DB in such format {token_count: N, llm_provider: "name", llm_model: "name", date: "date"}
2. add endpoint, that will calculate token usage for specified date, or range of dates
   2.1) possibly, if llm_provider==openai, we could, based on amount of tokens, calculate $ spent per date