feat(holiday-system): implement comprehensive holiday management features

- Added holiday types and organization holidays management with CRUD operations.
- Introduced country holidays import functionality using the date-holidays npm package.
- Created database migrations for holiday types and organization holidays tables.
- Developed a holiday calendar component for visual representation and management of holidays.
- Enhanced API routes for holiday-related operations and integrated them into the admin center.
- Updated frontend localization for holiday management features.
- Implemented scripts for populating holidays in the database for 200+ countries.

worklenz-frontend/public/locales/en/admin-center/overview.json

@@ -4,5 +4,33 @@
   "owner": "Organization Owner",
   "admins": "Organization Admins",
   "contactNumber": "Add Contact Number",
-  "edit": "Edit"
+  "edit": "Edit",
+  "holidayCalendar": "Holiday Calendar",
+  "addHoliday": "Add Holiday",
+  "editHoliday": "Edit Holiday",
+  "holidayName": "Holiday Name",
+  "holidayNameRequired": "Please enter holiday name",
+  "description": "Description",
+  "date": "Date",
+  "dateRequired": "Please select a date",
+  "holidayType": "Holiday Type",
+  "holidayTypeRequired": "Please select a holiday type",
+  "recurring": "Recurring",
+  "save": "Save",
+  "update": "Update",
+  "cancel": "Cancel",
+  "holidayCreated": "Holiday created successfully",
+  "holidayUpdated": "Holiday updated successfully",
+  "holidayDeleted": "Holiday deleted successfully",
+  "errorCreatingHoliday": "Error creating holiday",
+  "errorUpdatingHoliday": "Error updating holiday",
+  "errorDeletingHoliday": "Error deleting holiday",
+  "importCountryHolidays": "Import Country Holidays",
+  "country": "Country",
+  "countryRequired": "Please select a country",
+  "selectCountry": "Select a country",
+  "year": "Year",
+  "import": "Import",
+  "holidaysImported": "Successfully imported {{count}} holidays",
+  "errorImportingHolidays": "Error importing holidays"
 }