Implement Send bulk emails endpoint (Admin)

[janithlahirukariyawasam]

Description:
This issue involves implementing an API to Send bulk emails. The endpoint should allow Admin to make a POST request to {{baseUrl}}/api/admin/emails.

Tasks:

1. Create a controller for the /controllers/email endpoint in the backend (create the route email if not created).
2. Parse and validate the request body to ensure it matches the expected format.
3. Implement appropriate error handling and response status codes for different scenarios (e.g., validation errors, database errors).
4. Write unit tests to validate the functionality and correctness of the endpoint.

API documentation: https://documenter.getpostman.com/view/27421496/2s93m1a4ac#8744a3ee-970f-489a-853d-8b23fdee8de3

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

Acceptance Criteria:

• The profile API endpoint /controllers/email is implemented via a POST request.
• The request body is properly parsed and validated for the required format.
• 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.

Additional Information:
No

Related Dependencies or References:
No