Update example config/model_provider for "mistralai/mixtral-8x7b-instruct-v01" and add cached data

[jwmatthews]

• Update config.toml so the example references the current mixtral version: "mistralai/mixtral-8x7b-instruct-v01"
• Update model_provider to remove the older mixtral models no longer being served from BAM
• Update cached data from run_demo and mock_client for latest mixtral