Add minimal test for basic hackathon operations and enhance test utilities

- Introduced a new test module for hackathon-related functionality.
- Implemented a basic test for creating a hackathon using a mock repository.
- Enhanced the test utilities in `lib.rs` for better request handling and response extraction.
- Added a `ServiceClient` struct to facilitate HTTP requests in tests.
- Created a `RequestBuilder` to streamline building and sending requests with headers and JSON bodies.

imphnen-backend/src/bin/seed_test_submission.rs

@@ -342,6 +342,7 @@ async fn main() -> Result<(), Box<dyn Error>> {
             slides_url,
             technologies,
             submission_status,
+            judge_feedback: None,
             submitted_at: DateTime::parse_from_rfc3339(submitted_at)?.with_timezone(&Utc),
             is_deleted: false,
             created_at: Some(get_iso_date()),