Whisper configuration

Currently the parameters configuring whisper are hardcoded to be the same as the `whisper.cpp` cli.
This notably includes the sampling strategy and the maximum segment length.
Do we want to make this configurable?

Manual Experiments seem to indicate the `best_of` parameter of the `Greedy` sampling Strategy having a huge influence.

Interesting parameters:
- maximum segment length
- sampling strategy + configuration
- inital prompt
- ....

Start by tracing how Whisper configuration is passed to the whisper.cpp CLI, focusing on the defaults for sampling strategy, best_of, maximum segment length, and initial prompt. Define which parameters must become configurable and what user-facing configuration and behavior would count as complete.

Written by the indexing model from the issue text.