spanconfig: add periodic consistency checks between in-memory span config state and contents of system.span_configurations

**Describe the problem**

Every node in the system maintains an in-memory view over system.span_configurations using the KVSubscriber. The assumption is that this in-memory view matches the contents of the table correctly; however, in cases such as https://github.com/cockroachdb/cockroach/issues/110908, we've seen this not to be true. We should consider adding a periodic consistency checker that validates the in-memory view is correct.

cc @andrewbaptist

Jira issue: CRDB-35449