feat: 962 - link to add a discussion topic on the wiki (#963)

Impacted files:
* `user.dart`: added method `getUserWikiDiscussionPage`
* `user_management_test_prod.dart`: tested new method `getUserWikiDiscussionPage`

lib/src/model/user.dart

@@ -28,10 +28,24 @@ class User extends JsonObject {
   @override
   Map<String, dynamic> toJson() => _$UserToJson(this);
 
+  static String getUserWikiTag(final String userId) =>
+      '${userId.substring(0, 1).toUpperCase()}${userId.substring(1)}';
+
   static String getUserWikiPage(final String userId) => Uri(
         scheme: 'https',
         host: 'wiki.openfoodfacts.org',
-        path: 'User:'
-            '${userId.substring(0, 1).toUpperCase()}${userId.substring(1)}',
+        path: 'User:${getUserWikiTag(userId)}',
+      ).toString();
+
+  /// Link to add a discussion topic on the OpenFoodFacts wiki page of a user.
+  static String getUserWikiDiscussionPage(final String userId) => Uri(
+        scheme: 'https',
+        host: 'wiki.openfoodfacts.org',
+        path: 'index.php',
+        queryParameters: {
+          'title': 'User_talk:${getUserWikiTag(userId)}',
+          'action': 'edit',
+          'section': 'new',
+        },
       ).toString();
 }

test/user_management_test_prod.dart

@@ -192,6 +192,10 @@ void main() {
         User.getUserWikiPage('teolemon'),
         'https://wiki.openfoodfacts.org/User:Teolemon',
       );
+      expect(
+        User.getUserWikiDiscussionPage('tacinte'),
+        'https://wiki.openfoodfacts.org/index.php?title=User_talk%3ATacinte&action=edit&section=new',
+      );
     });
   });
 }