reports: generate reports without relying on gossiped system config

[ajwerner]

Is your feature request related to a problem? Please describe.
We currently generate reports on the system tenant in terms of sql concepts known to the zone-config layer. The KV layer learns about these updates via gossip today. We'd like to stop gossiping this data (#70560).

Describe the solution you'd like
Use a rangefeed-backed cache of the relevant system config data. See #70557 (comment).

Describe alternatives you've considered

Another approach would be to leverage span configs and augment the span configs with the relevant IDs needed for the reports. That has the benefit of being more space efficient. It doesn't necessarily extend back out to generating the reports in secondary tenants as well, though it's not clear we want that.

Additional context

Eventually we might want to generate such reports in secondary tenants (#70557). This is far from certain. If we did want that, we could leverage the approach here (for better or for worse), move the generation to a job, and run it in a sql pod.

Epic: CRDB-10489