Set up :snippet_edit_vue flag

The flag for Refactor Snippet edit form to Vue as described and
explained in the Epic: https://gitlab.com/groups/gitlab-org/-/epics/2679

lib/gitlab/gon_helper.rb

@@ -46,6 +46,7 @@ module Gitlab
       push_frontend_feature_flag(:monaco_snippets, default_enabled: false)
       push_frontend_feature_flag(:monaco_blobs, default_enabled: false)
       push_frontend_feature_flag(:monaco_ci, default_enabled: false)
+      push_frontend_feature_flag(:snippets_edit_vue, default_enabled: false)
     end
 
     # Exposes the state of a feature flag to the frontend code.