sql: split the hash_sharded_index test into two

In #16422, several new subtests were added to the hash_sharded_index
logic test. While the test is stable in local runs, the length of the
test is leading to flakiness when it is included in heavy workload
scenarios. To address this, this patch splits the subtests added in

Epic: none
Fixes: #162012

Release note: None

Author: eric-alton