E2E - automatically create incident for alert

What does this MR do and why?

Describe in detail what your merge request does and why.

New E2E test - with create incident setting enabled, a new alert will automatically create a new incident.

1. Login to gitlab
2. Create new project
3. Navigate to Settings -> Monitor -> Alerts
4. Open Alert settings tab
5. Enable Create an incident setting (select checkbox)
6. Save settings
7. Setup new integration (HTTP endpoint)
8. Send a test alert from this integration
9. Navigate to Monitor -> Incidents
10. Verify there is an incident in the project's incident list.

• There are also some refactoring to fit in the new flow for this test.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.