chore: merge 'dev' to staging

Description

I changed the route for the POST request from api/v1/newsletters/subscribers to api/v1/newsletter-subscriptions to better reflect the purpose of the endpoint. This change is part of an ongoing effort to improve the clarity and consistency of our API routes.

Related Issue (Link to issue ticket)

Motivation and Context

The previous route name api/v1/newsletters/subscribers was a bit ambiguous and could be misinterpreted as a route that manages only the subscribers. Changing it to api/v1/newsletter-subscriptions makes it clearer that this endpoint handles subscription actions, improving the overall API design.

How Has This Been Tested?

I updated the relevant unit tests to reflect the new route and ran them to ensure the change does not break existing functionality. I also manually tested the route using Postman to verify that the request and response are handled correctly.

Screenshots (if appropriate - Postman, etc):

Types of changes

[ ] Bug fix (non-breaking change which fixes an issue)
[ ] New feature (non-breaking change which adds functionality)
[X] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

[X] My code follows the code style of this project.
[X] My change requires a change to the documentation.
[X] I have updated the documentation accordingly.
[X] I have read the CONTRIBUTING document.
[X] I have added tests to cover my changes.
[X] All new and existing tests passed.

hngprojects / hng_boilerplate_python_fastapi_web