added webrtc versions consts

Author: Brazol

lib/stream_webrtc_flutter.dart

@@ -23,3 +23,6 @@ export 'src/native/android/audio_configuration.dart';
 export 'src/native/ios/audio_configuration.dart';
 export 'src/native/rtc_video_platform_view_controller.dart';
 export 'src/native/rtc_video_platform_view.dart';
+
+const String androidWebRTCVersion = '137.0.1';
+const String iosWebRTCVersion = '137.0.43';