[GREEN] Add shimmer loading effect to image_holder.dart

lib/component/image_holder.dart

@@ -2,6 +2,7 @@ import 'package:bisaGo/config/styles.dart';
 import 'package:bisaGo/flavor/flavor.dart';
 import 'package:cached_network_image/cached_network_image.dart';
 import 'package:flutter/material.dart';
+import 'package:shimmer/shimmer.dart';
 
 class ImageHolder extends StatelessWidget {
   final String url;
@@ -76,10 +77,12 @@ class ImageHolder extends StatelessWidget {
               fit: BoxFit.cover,
             )),
       ),
-      placeholder: (context, _) => const Center(
-          child: CircularProgressIndicator(
-        valueColor: AlwaysStoppedAnimation<Color>(greenPrimary),
-      )),
+      placeholder: (context, _) => Container(
+          child: Shimmer.fromColors(
+              baseColor: Colors.grey[300],
+              highlightColor: Colors.grey[100],
+              enabled: true,
+              child: Container())),
       errorWidget: (context, url, error) =>
           const Center(child: Icon(Icons.broken_image, color: Colors.black38)),
     );