feat(childManage): add goal management endpoints

📌 Description:

This PR introduces a complete CRUD implementation for managing Goals assigned to children within the Child Management module. The following features were added:

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✅ Added Endpoints:

• POST /api/child-management/goals: Create a new goal for a specific child and subject.
• PUT /api/child-management/goals/{goalId}: Update an existing goal by ID.
• DELETE /api/child-management/goals/{goalId}: Delete a goal by ID.
• GET /api/child-management/goals/child/{childId}: Retrieve all goals assigned to a specific child.

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📁 Changes Summary:

• GoalController: Implements all the goal-related REST APIs using GoalService.
• GoalDTO: Validated DTO for input/output mapping of goal data.
• ApiPaths.Goal: Centralized API paths to ensure consistency and maintainability.
• Added proper validation, error handling (via FunctionalException), and OpenAPI annotations for documentation.

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Closes IA-694