Move some arguments from load_model to transcribe(),...

[Barabazs]

i think 3 often used args task, language, initial_prompt should be moved from load_model() to transcribe() for compatibility with original whisper

related: #191 #259

Originally posted by @phineas-pta in #241

I've also noticed many users wanting to pass/change specific parameters after loading the model.
It might be interesting to see if this is indeed needed and produces a better user experience.

fwiw, the current use of dicts for settings makes it hard to track which option is appropriate in any of the methods. Migrating from dicts to Pydantic models might be good idea.