Push highlight_js feature flag to frontend

Pushes the highlight_js FF to the frontend

app/controllers/projects/tree_controller.rb

@@ -19,6 +19,7 @@ class Projects::TreeController < Projects::ApplicationController
     push_frontend_feature_flag(:lazy_load_commits, @project, default_enabled: :yaml)
     push_frontend_feature_flag(:new_dir_modal, @project, default_enabled: :yaml)
     push_frontend_feature_flag(:refactor_blob_viewer, @project, default_enabled: :yaml)
+    push_frontend_feature_flag(:highlight_js, @project, default_enabled: :yaml)
   end
 
   feature_category :source_code_management