[FEATURE] Ability to add extra information in BetterPlayerDataSource

[rupinderjeet]

Is your feature request related to a problem? Please describe. No.

Describe the solution you'd like I would like BetterPlayerDataSource class to optionally receive a dynamic variable tag. The library doesn't need to do anything with this variable other than making it public and final. A tag can be anything from just a identifier to a model with extra information.

Describe alternatives you've considered There is another option to just set a Map of extra values on data-source, but I think a dynamic variable is more flexible.

Additional context just_audio's UriAudioSource supports this. Here are the related docs.