Add track metada informations

[ThePedroo]

Changes

This adds a metadata field into track in TrackStartEvent with information about the playing file.

Why

This allows the bot/client to be more aware of what's happening internally, also allows easier debugging of some audio quality issues. This is PR is connected with #42

Checkmarks

• [x] The modified endpoints have been tested.
• [x] Used the same indentation as the rest of the project.
• [x] Still compatible with LavaLink clients.

Additional information

There are issues on how sources like http will have its bitrate calculated, as till TrackEndEvent, the length is unknown due to leak of such calculations, which is done outside by FFmpeg.