Mistral: Mistral API specs docs materially updated

{ "choices" : [ { "finish_reason" : "stop" , "index" : "0" , "message" : { } } ] , "created" : "1702256327" , "id" : "cmpl-e5cc70bb28c444948073e77776eb30ef" , "model" : "mistral-small-latest" , "object" : "chat.completion" , "usage" : { } }