Add file inspect service function

[garyzhang99]

Description

Add service functions so that our LLM model can inspect local .pdf .docx .xlsx files. Also add a inspect_file_as_text service function that include all the file inspection function.

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