Add cli for downloading models

[nezhar]

This PR proposes an aditional console script for downloading models.

(venv) nezhar@nezhar:~/DEV$ whisper-download --help
usage: whisper-download [-h]
                        [--model {tiny.en,tiny,base.en,base,small.en,small,medium.en,medium,large-v1,large-v2,large}]
                        [--model_dir MODEL_DIR]

options:
  -h, --help            show this help message and exit
  --model {tiny.en,tiny,base.en,base,small.en,small,medium.en,medium,large-v1,large-v2,large}
                        name of the Whisper model to use (default: small)
  --model_dir MODEL_DIR
                        the path to save model files; uses ~/.cache/whisper by
                        default (default: None)

Example usage:

(venv) nezhar@nezhar:~/DEV$ whisper-download --model tiny --model_dir whisper_models
100%|█████████████████████████████████████| 72.1M/72.1M [00:45<00:00, 1.66MiB/s]
(venv) nezhar@nezhar:~/DEV$ ls -la whisper_models/
total 73816
drwxrwxr-x  2 nezhar nezhar     4096 Dez 31 16:53 .
drwxrwxr-x 27 nezhar nezhar     4096 Dez 31 16:53 ..
-rw-rw-r--  1 nezhar nezhar 75572083 Dez 31 16:54 tiny.pt