Fix issue #86: Create winners view

[cld-vasconcelos]

This pull request fixes #86.

The issue has been successfully resolved. The changes introduced a new endpoint /winners/ that returns the required data about contest winners. The WinnersView class was added to handle GET requests, querying the ContestSubmission model to retrieve contests with winners. The data is annotated to include the contest title, description, end date, winner's name, and the winning photo, and is ordered by the contest end date as specified. A serializer WinnerSerializer was created to define the structure of the response. Additionally, a test case WinnersViewTest was implemented to verify that the endpoint returns the correct data, confirming the functionality with assertions on the response content. These changes collectively address the issue requirements.

Automatic fix generated by OpenHands 🙌

[cld-vasconcelos]

OpenHands started fixing the pr! You can monitor the progress here.

[cld-vasconcelos]

OpenHands successfully implemented the contest_winners API endpoint, fulfilling all requirements. The endpoint uses efficient database querying with Django's F expressions and returns a JSON response as specified. All issues appear resolved.