[FE] Add 'disable autogenerated subtitles' toggle

[martinhoyer]

I'm sure I'm notthe only one who would greatly appreciate an option to disable autogenerated subtitles.

use case: if selected language subtitles exist and are not auto generated = display subtitles; else don't

problem: I like to have english subtitles available for many videos, especially educational. However, when en subtitles are not available, there is usually auto-generated garbage(which is really only useful for hearing impaired), or even chinese/other random language

[itgoyo]

this is a good idea,I approve of it.