feat: Ability to delete all threads

[Noam-Br]

Problem
Right now I have to delete each thread separately, I'd like to clear out all threads

Success Criteria
All threads are cleaned at a single click

Additional context
Same feature that has in ChatGPT:

[Van-QA]

We will consider it, for now, you can delete all threads manually by going to the Jan data folder and deleting all of these thread folders

[Noam-Br]

Got it will do for now. Thanks @Van-QA!