[WIP] Add prompt tuning module

[DavdGao]

Description

Add a prompt tuning module, which provides functions:

• System prompt generation (with few-shot examples)
• System prompt tuning

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