Fix user namespaces without routes

GitLab uses routes records for non-GET /admin/users/USERNAME requests to identify requested user record. If user record has no related record in routes table, which is data integrity issue, the Admin will get 404 response.

The customers have reported the above data integrity issues with their instances and we have observed the same on gitlab.com. See https://console.postgres.ai/gitlab/gitlab-production-main/sessions/29086/commands/90575.

We need to ensure that we have no user namespace without a corresponding route and then rebuild the missing namespaces for the above.

Workaround

Fix customer data with this script.

Implementation plan

TBD