openImageInFullScreenMode method
Implementation
openImageInFullScreenMode(
    String? imageUrl, CometChatTheme theme, BuildContext context) {
  if (imageUrl != null || imageUrl!.isNotEmpty) {
    Navigator.push(
        context,
        MaterialPageRoute(
            builder: (context) => ImageViewer(
                  imageUrl: imageUrl,
                  backgroundColor: theme.palette.getBackground(),
                  backIconColor: theme.palette.getPrimary(),
                )));
    debugPrint('thumbnail on click');
  }
}