Mark WITH RECURSIVE queries as read-only

What does this MR do and why?

Marks CTEs as read-only:

> pat_family.update_all(revoked: true)
ActiveRecord::ReadOnlyRecord: This relation is marked as read-only

However, it allows using the CTE in a subquery:

> PersonalAccessToken
  .where(id: pat_family.pluck_primary_key)
  .update_all(revoked: true)
=> 1

Follow-up to gitlab-com/gl-infra/production#16047 (comment 1475636660).

Related to #419012 (closed).

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