[FEATURE] Add support for true open-source models like MPT

[casper-hansen]

Add support for MPT models, which are licensed under Apache 2.0 just light LightLLM.

They have 7B and 30B with different context lengths, here is one of them:
https://huggingface.co/mosaicml/mpt-7b-8k

[shihaobai]

@casperbh96 Thank for your attention. We will add this model.