Add option to change name of subtitles file

[Mrtenz]

I'm having an issue similar to #131 where Plex doesn't detect the generated subtitles. It seems to be fixed by renaming it to just .en.srt. In addition, I'm using Bazarr but not with Subgen directly, as I mainly use the batch endpoint for generating subtitles (yes, weird set up, but I only need to generate subtitles for certain shows, which is not easy with Bazarr directly). Bazarr doesn't detect the .subgen.large-v3.en.srt files either, but does detect .en.srt files.

The problem with renaming the files manually is that the next time I run Subgen, it wouldn't detect the subtitles and generate them again. It would be nice if there was an option to change the name of the file to be just .[language].srt.

[McCloudS]

The issue you linked provides a solution to fix plex not detecting them: https://github.com/McCloudS/subgen/issues/131#issuecomment-2442043532

I can think on a way to add comfortable renaming so Bazarr plays nicely. The simplest way right now is manually editing https://github.com/McCloudS/subgen/blob/b1e2bb2fdf41af14861612965ccd545acd55d470/subgen.py#L83