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/en/settings/ratecard-settings.json

@@ -48,5 +48,8 @@
   "jobTitleCreatedSuccess": "Job title created successfully",
   "jobTitleCreateError": "Failed to create job title",
   "createButton": "Create",
-  "cancelButton": "Cancel"
+  "cancelButton": "Cancel",
+  "discardButton": "Discard",
+  "manDaysCalculationMessage": "Organization is using man days calculation ({{hours}}h/day). Rates above represent daily rates.",
+  "hourlyCalculationMessage": "Organization is using hourly calculation. Rates above represent hourly rates."
 }