Employee Module | Add Employee

- [x] Employee Model
- [x] Employee Validator - add employee
- [x] Employee Dao - add employee
- [x] Employee Service - add employee

## Issue Title: Implement "Add Employee" Functionality in Employee Module

### Issue Description

We need to implement the "Add Employee" functionality within the Employee Module. This involves creating the Employee Model, adding validation in the Employee Validator, and implementing the necessary methods in the Employee Dao and Employee Service.

### Task Breakdown

1. **Employee Model:**
- Create a new Employee model class if it doesn't already exist.
- Define the attributes and properties that an employee should have, such as name, employee ID, contact information, etc.

2. **Employee Validator:**
- Enhance the Employee Validator to include validation rules for adding an employee.
- Ensure that the input data meets the required criteria, such as non-empty name, valid contact details, etc.
- Provide informative error messages for invalid inputs.

3. **Employee Dao:**
- Implement the "addEmployee" method in the Employee Dao class.
- This method should take an Employee object as a parameter and add it to the database or data store.
- Handle any potential exceptions gracefully and provide clear error messages.

4. **Employee Service:**
- Create an "addEmployee" service method in the Employee Service class.
- This method should serve as an intermediary between the Validator and Dao.
- Validate the input employee data using the Employee Validator.
- If the data is valid, call the "addEmployee" method in the Employee Dao to add the employee.
- Return appropriate responses to indicate success or failure.

### Additional Information

Please consider the following guidelines while working on this issue:
- Follow the coding conventions and best practices of the project.
- Ensure that unit tests are written and that the new functionality is thoroughly tested.
- Document any changes made to the codebase.
- Create meaningful commit messages that reference this issue for better traceability.

This issue is part of the overall effort to enhance the Employee Module's functionality. Please feel free to ask for clarification or assistance if needed.