Introducing RAG module into package

[ZiTao-Li]

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Introducing RAG module into AgentScope package

Description

Introducing retrieval augmented generation techniques into AgentScope package to enrich the ability of agents.

To accommodate the RAG process of different packages, we abstract the RAG process into four stages:

• data loading: loading data into memory for following processing;
• data indexing and storage: document chunking, embedding generation, and off-load the data into VDB;
• data retrieval: taking a query and return a batch of documents or document chunks;
• post-processing of the retrieved data: use the retrieved data to generate an answer.

Checklist

Please check the following items before code is ready to be reviewed.

• Code has passed all tests
• Docstrings have been added/updated in Google Style
• Documentation has been updated
• Code is ready for review

[xieyxclack]

Please see the inline comments, thx

[DavdGao]

Please see inline comments

[DavdGao]

Plz see inline comments, and I think the RAG module is still not ready for using.

1. For me, I cannot find how to set rag_config in docstring and example: what parameters should be included and their constraints, and what format should the parameters follow.
2. RAG-related documents are suggested, maybe add a RAG section in tutorial.

[DavdGao]

lgtm