[Enhancement]: Support SRT files for audio books

[akabhirav]

Describe the feature/enhancement

I have only recently started using AudioBook shelf with audio files generated from text files. I am confident that generating SRT files would not be too difficult, either using some Speach to Text tool on my library or while generating the Audio itself.

It would be great if AudioBook shelf is able to recognize and map SRT files with audio book tracks and the player is able to display the subtitles when we play the video

This will be good both from an accessbility and usability point of view. This would also go for the mobile players but once server supports this.