Implemented feature flag incident management

Added a feature flag to as part of the incident management rollback strategy

• Added a new feature flag incident_management_features_disabled
• Moved incident management menu item behind feature flag
• Moved controller index action behind feature flag
• Added test coverage
• Fixed existing specs failing due to new feature flag changes

References

Related issue Related issue

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:incident_management_features_disabled, @project)

2. Visit projects
3. Select project where feature flag is enabled for
4. Click on Monitor menu on the left sidebar
5. Check that Incident menu tab does not show up
6. Visit the incident list page directly
7. Check that it return 404 page

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist.