[video_player] Added new field observeAppLifecycle to enable background playing of v…

packages/video_player/video_player/lib/video_player.dart

@@ -247,7 +247,8 @@ class VideoPlayerController extends ValueNotifier<VideoPlayerValue> {
   /// Attempts to open the given [dataSource] and load metadata about the video.
   Future<void> initialize() async {
     _lifeCycleObserver = _VideoAppLifeCycleObserver(this);
-    _lifeCycleObserver.initialize();
+    if (videoPlayerOptions?.observeAppLifecycle)
+      _lifeCycleObserver.initialize();
     _creatingCompleter = Completer<void>();
 
     DataSource dataSourceDescription;

packages/video_player/video_player_platform_interface/lib/video_player_platform_interface.dart

@@ -348,6 +348,12 @@ class VideoPlayerOptions {
   /// The default value is false
   final bool mixWithOthers;
 
+  /// Set this to true to let plugin manage play/pause with app lifecycle changes,
+  /// Set this to fase to keep playing video in background, when app goes in background
+  /// The default value is true
+  final bool observeAppLifecycle;
+
   /// set additional optional player settings
-  VideoPlayerOptions({this.mixWithOthers = false});
+  VideoPlayerOptions(
+      {this.mixWithOthers = false, this.observeAppLifecycle = true});
 }