feat(admin-center): implement admin center settings retrieval and enhance holiday population logic

- Added a new API endpoint in AdminCenterController to fetch admin center settings, including organization details.
- Updated the admin center API router to include the new settings route.
- Enhanced the holiday controller to check for recent holiday population before attempting to repopulate, preventing duplicate entries.
- Improved the holiday calendar component to manage holiday population attempts and display loading states.
- Updated localization files to support new messages related to calculation methods and holiday settings.

worklenz-frontend/public/locales/zh/settings/ratecard-settings.json

@@ -48,5 +48,8 @@
   "jobTitleCreatedSuccess": "职位名称创建成功",
   "jobTitleCreateError": "职位名称创建失败",
   "createButton": "创建",
-  "cancelButton": "取消"
+  "cancelButton": "取消",
+  "discardButton": "放弃",
+  "manDaysCalculationMessage": "组织正在使用人日计算（{{hours}}小时/天）。上述费率代表日费率。",
+  "hourlyCalculationMessage": "组织正在使用小时计算。上述费率代表小时费率。"
 }