Parse external subtitles

[zoriya]

Feature description

The scanner should be able to retrieves external subtitles files and the /info of the trancoder should list them as well (maybe the scanner can ignore them and the transcoder could just check for them?)

[JeWe37]

It would also be nice if this supported subtitle titles, languages and tags(sdh, cc, hi, forced, default) like jellyfin. MKS file support would also be helpful for bypassing potentially long subtitle extraction times poorly muxed large files.