feat(holiday-calendar): implement holiday calendar component with CRUD functionality

- Added a new `HolidayCalendar` component for managing custom and official holidays.
- Integrated holiday type fetching and population logic to streamline holiday management.
- Enhanced UI with modals for creating, editing, and deleting holidays, including validation and user feedback.
- Updated styles for improved visual presentation and user interaction.
- Refactored sidebar and routes to accommodate new component structure and localization updates.

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

@@ -4,6 +4,6 @@
   "teams": "Teams",
   "billing": "Billing",
   "projects": "Projects",
-  "settings": "Settings",
+  "settings": "Utilization Settings",
   "adminCenter": "Admin Center"
 }