Create dast_failed_site_validations feature flag

ee/app/controllers/projects/security/dast_profiles_controller.rb

@@ -8,6 +8,7 @@ module Projects
       before_action do
         authorize_read_on_demand_scans!
         push_frontend_feature_flag(:dast_saved_scans, @project, default_enabled: :yaml)
+        push_frontend_feature_flag(:dast_failed_site_validations, @project, default_enabled: :yaml)
       end
 
       feature_category :dynamic_application_security_testing

ee/config/feature_flags/development/dast_failed_site_validations.yml

+---
+name: dast_failed_site_validations
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/56146
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/323961
+milestone: '13.10'
+type: development
+group: group::dynamic analysis
+default_enabled: false