Proposal: Android add config for enable or disable adding image/video to gallery

[akindone]

For some situation, app download image or video but not intended to add to gallery, can make this a config for task? https://github.com/fluttercommunity/flutter_downloader/blob/f5a7b0acb5f8c43f77d2375d0f6e13fa35cc14f8/android/src/main/java/vn/hunghd/flutterdownloader/DownloadWorker.java#L421