fix(android): prevent livestream failures by assigning a default user-agent for Media3 requests

[tomislav-arambasic]

Added a custom user-agent string to prevent 403 errors when playing Live365 streams using Media3.

Resolves #2495.

Issue

Some streams require user-agent to be defined. Such as
https://streaming.live365.com/a39417 & https://streaming.live365.com/a62429.
Starting those streams with new media3 implementation resulted in playback error

{
    "message": "Source error",
    "code": "android-io-bad-http-status"
}

Tested in example app, on various emulators, physical devices and on different Android versions & Android Studio versions... Same issue everywhere.
main branch did work as expected, streams played in all scenarios.

After looking into it, server was throwing 403 - Forbidden for media3 implementation.

Native error in media3 exoplayer:

Fix

Added default user-agent to comply with those restrictions.

Users are still able to override user-agent, by defining it inside track object.

Example:

{
    "url": "https://das-edge11-live365-dal03.cdnstream.com/a39417",
    "title": "Radio Stream 1",
    "artist": "Not Working",
    "artwork": "https://rntp.dev/example/smooth-jazz-24-7.jpeg",
    "isLiveStream": true,
    "userAgent": "TestUserAgent"
  }

Verified in example app, running on Motorola g34 5G, Android 14.

[jspizziri]

@tomislav-arambasic this is great! Thanks for running this down and doing the work to resolve it. I've left some feedback.