FEATURE REQUEST: Add Input Validation and Improve Error Handling for Appointment API

### Is your feature request related to a problem?

- [x] Yes, it is related to a problem

### Describe the feature you'd like

## 🌟 Feature Description
Implement input validation and improve error handling for the appointment-related API endpoints.

## 🔍 Problem Statement
The current appointment API lacks input validation, allowing invalid or incomplete data to be processed. Additionally, the error handling is generic, making it difficult to identify specific issues with requests

## 🎯 Expected Outcome
Add Cerberus validation to ensure that appointment data such as date, time (AM/PM format), and status are correctly formatted.Enhance error handling to provide detailed error messages, like "Invalid appointment ID" or "Missing required fields", instead of vague error responses.

### Record

- [x] I agree to follow this project's Code of Conduct
- [x] I want to work on implementing this feature