Include e2e tests for public endpoints

[jeroenrinzema]

This PR includes e2e tests using testcontainers for the currently exposed endpoints within the Nexus service.

[Copilot]

Pull request overview

This PR adds end-to-end tests for the Nexus service's public endpoints using testcontainers. The implementation includes a new PostgreSQL container helper, test files for campaign and template controllers, and necessary database store modifications to support test data creation. The changes also include enhanced error handling for "not found" scenarios in the API controllers.

• Added e2e tests using testcontainers for campaigns and templates endpoints
• Introduced PostgreSQL testcontainer helper for isolated database testing
• Enhanced error handling to properly return 404 responses for missing resources

Reviewed changes

Copilot reviewed 9 out of 10 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
services/nexus/internal/store/projects.go	Added CreateProject method and updated field ordering in Project struct; modified GetProject query to explicitly list columns
services/nexus/internal/http/controllers/v1/templates_test.go	Added e2e test for GetTemplate endpoint with found/not found scenarios
services/nexus/internal/http/controllers/v1/templates.go	Added explicit handling for sql.ErrNoRows to return 404 responses
services/nexus/internal/http/controllers/v1/http_test.go	Added shared DefaultProject test fixture
services/nexus/internal/http/controllers/v1/campaigns_test.go	Added comprehensive e2e tests for all campaign endpoints
services/nexus/internal/http/controllers/v1/campaigns.go	Added explicit handling for sql.ErrNoRows to return 404 responses
pkg/http/problem/problem.go	Enhanced comment clarity for the Describe function's error wrapping behavior
pkg/container/postgres.go	Added RunPostgreSQL helper to create isolated test databases using testcontainers
go.mod	Added testcontainers and related dependencies; updated various dependency versions

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