Add support for specifying the number of speakers in ASRDiarizationPipeline

Hi @speechbox developers,

I've been using the `ASRDiarizationPipeline` and noticed that there isn't a built-in option to specify the number of speakers when performing diarization. This feature would be very helpful for scenarios where the number of speakers is already known or can be estimated beforehand, as it can potentially improve the performance of the speaker diarization process.