Implement Update Salary

<UserStory>EMP08: Update Salary Details</UserStory>

<Changes>
- Added `updateSalary` method in ZenvyController to connect payroll updates with PayslipManagementService
- Implemented `PayslipManagementService::updateSalary` with employee existence and Finance-role authorization checks
- Extended Payroll model with setter methods for salary components
- Improved error handling with clear runtime exceptions for invalid index selection, unauthorized access, and missing employees
</Changes>

<Review>
Smitha Mohan
</Review>

Trenser.Zenvy/Trenser.Zenvy/services/PayslipManagementService.h

@@ -1,5 +1,7 @@
 #pragma once
-#include "DataStore.h"
+#include <string>
+#include<stdexcept>
+#include"DataStore.h"
 
 class PayslipManagementService
 {
@@ -7,4 +9,5 @@ private:
 	DataStore& m_dataStore;
 public:
 	PayslipManagementService() : m_dataStore(DataStore::getInstance()) {};
+	void updateSalary(const std::string&, const double, const double, const double, const double, const double);
 };