Db-gpt

What's Changed
- Built-in database query plugin, supports automatic data querying. yhjun1026
- Support milvus vector storage. Aries-ckt
- Update the docs use readthedocs. csunny
- Add lint for source code yihong0618

Add docs for DB-GPT project. the project url is there: [db-gpt.readthedocs.io](https://db-gpt.readthedocs.io/)

Multi llm model support:
- model_adapter for load multi models
- chat_adapter for chat with models.
Supports multiple large language models, currently supporting Vicuna (7b, 13b), ChatGLM-6b (int4, int8)

多模型支持：
- 新增Model Adapter 以及Chat Adapter， 后续可以通过实现adapter接入更多大模型
- 只是库支持ChatGLM-6b

New Feature:
1. Add Local Knownledge Embedding.
2. DB-GPT-Plugins: sql_executor, auto_chart.

fix same bugs