Add createLabel to NamespacePermissions

What does this MR do and why?

The work item metadata query reads NamespacePermissions.adminLabel only to decide whether to show a "Create label" button. This adds createLabel next to it and moves the frontend to the new field. adminLabel stays as it is and still checks admin_label, since clients outside the web UI can query it. Nobody gains or loses access, since Reporter and Planner hold both permissions.

• NamespacePermissions has a new createLabel field.
• Both work_item_metadata.query.graphql files and work_item_metadata_provider.vue read createLabel.
• The GraphQL reference docs and the introspection files are regenerated.

References

• https://gitlab.com/gitlab-org/gitlab/-/work_items/565525
• Review question this answers !257926 (comment 3966374523)

Screenshots or screen recordings

No UI change.

How to set up and validate locally

bundle exec rspec spec/graphql/types/permission_types/namespaces/base_spec.rb
yarn jest spec/frontend/work_items/components/work_item_metadata_provider_spec.js spec/frontend/work_items/components/work_item_labels_spec.js ee/spec/frontend/work_items/components/work_item_labels_spec.js

MR acceptance checklist

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