Add extensions for Matroska MIME Types

[Bradez]

This PR defines the extensions for the Matroska container format mime type.

There are four extensions, albeit only three of them are defined within here in compliance with the IANA assignment in RFC9559:

• mka is for audio and is assigned audio/matroska;
• mkv is for video and is assigned video/matroska;
• mk3d is for stereoscopic video and is assigned video/matroska-3d; and finally
• mks is for subtitles, albeit instead of using the previously (and now deprecated) video/x-matroska mime type it is now recommended to to use application/octet-stream given that mks is in fact not a video. Despite this, I have opted intentionally not to include mks as an extension of application/octet-stream due to its broad (fallback) scope.

[OskarStark]

Thank you