Issue #3519433: Fix URL structure of admin pages

modules/ad_content/src/Entity/AdContent.php

@@ -43,12 +43,12 @@ use Drupal\user\EntityOwnerTrait;
  *   admin_permission="administer ads",
  *   field_ui_base_route = "entity.ad_content.collection",
  *   links = {
- *     "add-form" = "/ad/content",
- *     "create" = "/ad/content",
- *     "canonical" = "/ad/content/{ad_content}",
+ *     "add-form" = "/admin/ad/content/add",
+ *     "create" = "/admin/ad/content/add",
+ *     "canonical" = "/admin/ad/content/{ad_content}",
  *     "collection" = "/admin/ad",
- *     "delete-form" = "/ad/content/{ad_content}/delete",
- *     "edit-form" = "/ad/content/{ad_content}/edit",
+ *     "delete-form" = "/admin/ad/content/{ad_content}/delete",
+ *     "edit-form" = "/admin/ad/content/{ad_content}/edit",
  *   },
  *   entity_keys = {
  *     "id" = "id",