make it a library with a CLI

[emilianobonassi]

Is your feature request related to a problem? Please describe. Simplify UX and use it as a library in other projects (e.g. clients)

Describe the solution you'd like A simple refactor as CLI + Python Library.

Describe alternatives you've considered No other alternatives were currently explored.

Additional context Original scripts ingest.py and privateGPT.py should keep the same interface to not break current usage.