[WIP] Add direct prompt tuning modules

[garyzhang99]

Description

According to the current discussion, the prompt tuning we could try to implement include:

• [ ] a direct prompt tuning module(input: user_prompt, output: optimized prompt)
• [ ] a system prompt note adding moduel(input: system_prompt + dialog_history, output: notes to be added to system_prompt)
• [ ] an example selection module

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