#66348 outlined a scheme to support zone configs for secondary tenants, the MVP for which we implemented as part of #67679. One part left out of the MVP was replacing our use of the system config span in the optimizer (which is the only remaining blocker for enabling locality-aware planning for secondary tenants).

The optimizer uses zone configs to generate locality optimized plans. Today it uses the gossiped SystemConfigSpan data to access the descriptor's (potentially stale) zone config.
(a) This information only available for the host tenant, and
(b) We want to stop gossiping the system config span (see the RFC).

To continue providing the optimizer access to zone configs, we could cache them in the catalog layer and associate them with their descriptors.

Epic: CRDB-10489