## Problem
Pagebench creates a bunch of tenants by first creating a template tenant
and copying its remote storage, then attaching the copies to the
Pageserver.
These tenants had custom configurations to disable GC and compaction.
However, these configs were only picked up by the Pageserver on attach,
and not registered with the storage controller. This caused the storage
controller to replace the tenant configs with the default tenant config,
re-enabling GC and compaction which interferes with benchmark
performance.
Resolves#11381.
## Summary of changes
Register the copied tenants with the storage controller, instead of
directly attaching them to the Pageserver.