examples : add --print-confidence option to cli (#3150)

examples : add --print-confidence option to cli (#3150)

* examples : add --print-confidence option to cli

This commit adds a new command-line option `--print-confidence` to the
whisper-cli. When enabled, this option prints the confidence level of each
token in the transcribed text using ANSI formatting codes.

The confidence levels are represented using different styles:
```console
main: confidence: highlighted (low confidence), underlined (medium), dim (high confidence)
```

Refs: https://github.com/ggml-org/whisper.cpp/issues/3135