Implement the mentor availability endpoint

[anjula-sack]

Description

This issue involves implementing the Mentor availability API endpoint. The endpoint should allow clients to make a POST request to {{baseUrl}}/api/me/availability and provide availability in the request body.
sample request body:

{
    "availability": true
}

Tasks

1. Create a controller for the /controllers/mentors endpoint in the backend.
2. Parse and validate the request body to ensure it matches the expected format.
3. Store the mentor's availability in the database.
4. Implement appropriate error handling and response status codes for different scenarios (e.g., validation errors, database errors).
5. Write unit tests to validate the functionality and correctness of the endpoint.

API documentation: https://documenter.getpostman.com/view/27421496/2s93m1a4ac#3eeb0372-4e07-4a2a-b72d-114d8639783d

ER diagram: https://drive.google.com/file/d/11KMgdNu2mSAm0Ner8UsSPQpZJS8QNqYc/view

Acceptance Criteria

• The Mentor API endpoint /controllers/mentors is implemented and accessible via a PUT request.
• The request body is properly parsed and validated for the required format.
• The mentor's availability is stored correctly in the database or data store.
• Appropriate error handling is implemented, providing meaningful error messages and correct response status codes.
• Unit tests are written to validate the functionality and correctness of the endpoint.

[anjula-sack]

#64