Added whisperX support

[DennisTheD]

I added support for the whisperX engine. The engine can be activated by setting the ASR_ENGINE to "whisperx". In order to use the diarization pipeline, a Huggingface access token needs to be supplied, using the "HF_TOKEN" variable. You also need to accept some user agreements (see https://github.com/m-bain/whisperX for further details). If you do not need diarization, the token is not required.