[FEAT] QD base code additions

[kevinl424]

• query decomposition initial code
• only notebooks included

[kevinl424]

Thanks for adding all this previous work! Could you provide explanations for each file?

File Breakdown

• langchain_ms.ipynb - using LangChain to breakdown subqueries
• MS_finetuning.ipynb - fine-tuning the query decomposition
• rest - multi step query decomp examples