[Feature Request]: Add function to add external subtitles

[Eibyx]

Preflight checklist

• I have searched the issue tracker for a bug report that matches the one I want to file, without success.
• I have searched the features list for this feature, and I couldn't find it.
• I have checked that I'm using the latest stable version of the app.

Problem Description

There are animes that do not have Spanish subtitles, I translate subtitles from English or Japanese to Spanish but there is no option to add external subtitles.

Proposed Solution

Add the option for the VLC application to add subtitles from the phone storage.