spanconfig: tooling for looking up span configs

As we saw in a recent escalation (https://github.com/cockroachlabs/support/issues/3222), looking up span configs in a multi-tenant cluster is not very straightforward. We used this query for a range with `/Tenant//Table/`:

```
select crdb_internal.pretty_key(start_key, -1), crdb_internal.pretty_key(end_key, -1), crdb_internal.pb_to_json('cockroach.roachpb.SpanConfig', config) from system.span_configurations where crdb_internal.pretty_key(start_key, -1) like '/Tenant//Table/%';
```

This results is a span config that doesn't include span config bounds since those are applied at a higher layer (e.g. in the allocator).

We need better tooling to make this lookup easier and to include span config bounds.

Jira issue: CRDB-49026

Epic CRDB-2245