FEAT: Audio Converters for speed, white noise, echo, and volume

[petebryan]

Description

Added new audio convertors to add the following:

• Change the speed of an audio file without altering pitch AudioSpeedConverter
• Add whitenoise over an existing audio file AudioWhiteNoiseConverter
• Add an echo to an existing audio file AudioEchoConverter
• Adjust volume of an audio file by scaling the amplitude. AudioVolumeConverter

Sorry I did not raise an issue for this ahead of time, experimentation of ideas turned into code and wanted to contribute. Happy to refactor whoever is deemed best.

Tests and Documentation

• Added unit tests for all convertors to test functionality and ensure audio transformations do not adversely affect audio files.
• Updated convertor documentation .py files to reflect these updates then ran jupytext --execute --to notebook to generate notebooks.