Currently, we use the [`work_item_rest_api`](https://gitlab.com/gitlab-org/gitlab/-/work_items/588874) feature flag to determine whether the backend REST APIs for work items are exposed. As we move closer to a global rollout, we should consider splitting this FF into seperate flags to enable the listing query to be exposed independently of the remaining endpoints. This enables development of those endpoints to continue, while unblocking the rollout of https://gitlab.com/gitlab-org/gitlab/-/work_items/596882, which depends on the listing endpoints on ~backend