added edit bookmark capabilities

lib/model/bookmark.dart

@@ -32,4 +32,14 @@ class Bookmark {
     'description': description,
     'createdAt': createdAt,
   };
+
+  Bookmark copyWith({String? link, String? name, String? description}) {
+    return Bookmark(
+      collectionId: collectionId,
+      name: name ?? this.name,
+      link: link ?? this.link,
+      description: description ?? this.description,
+      createdAt: createdAt,
+    );
+  }
 }