VSN-2012/ Add department name to DriverPlanningDTO from Admin Service
- Added 'department' field to DriverPlanningDTO.
- Updated getAllDriversForPlanning() to fetch the department name from Admin Service using driver.departmentId.
- Enriched DTO with department information for better display in planning UI.
- Ensured null-safety: if departmentId is null or Admin Service fails, department field remains null.