perf: intelligently enable global_reads (12% throughput TPC-C)

In instances where a table is read-only (and more generally, read-mostly), there are significant advantages in enabling `global_reads`, which prevent the need to read from the leaseholder. In TPC-C, the `ITEM` table contains 100,000 items which are never modified once inserted. In benchmark runs (using BenchBase), enabling `global_reads` on the `ITEM` table yields a 12% throughput improvement (50 WH, 45 clients, 3 node cluster).

We should investigate methods for sampling table accesses and, in cases where a table is found to be read-only (or read-mostly), enable `global_reads` until the next sampling interval.

Jira issue: CRDB-49431