Added the source_editor_toolbar feature flag

config/feature_flags/development/source_editor_toolbar.yml

+---
+name: source_editor_toolbar
+introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/82304
+rollout_issue_url: https://gitlab.com/gitlab-org/gitlab/-/issues/354748
+milestone: '14.9'
+type: development
+group: group::editor
+default_enabled: false

lib/gitlab/gon_helper.rb

@@ -58,6 +58,7 @@ module Gitlab
       push_frontend_feature_flag(:new_header_search, default_enabled: :yaml)
       push_frontend_feature_flag(:bootstrap_confirmation_modals, default_enabled: :yaml)
       push_frontend_feature_flag(:sandboxed_mermaid, default_enabled: :yaml)
+      push_frontend_feature_flag(:source_editor_toolbar, default_enabled: :yaml)
     end
 
     # Exposes the state of a feature flag to the frontend code.