Feature: Implement CRUD Endpoints for Templates in Letter Service

[f-s-h]

Implement the following endpoints:

Method	Endpoint	Success Code	Error Codes	Description
POST	/templates	201 Created	400	Creates a template.
GET	/templates	200 OK	400	Retrieves a list of all templates. Only return most important information of template.
GET	/templates/{id}	200 OK	400, 404	Retrieves a specific sport by its ID. Only return most important information of template.
GET	/templates/{id}/details	200 OK	400, 404	Retrieves a specific sport by its ID. Return the entire template.
PUT	/sports/{id}	204 No Content	400, 404	Updates an existing template by its ID.
DELETE	/sports/{id}	204 No Content	400, 404	Deletes a specific template by its ID.

• Protocol: JSON over HTTP.
• Headers: All requests sending data and all responses must include Content-Type: application/json.
• Error Payloads: 400 Bad Request and 404 Not Found responses must return a plain JSON object containing error details (e.g., {"error": "Template not found"}).