storage: benchmark and verification tool

[skyzh]

As our SQL layer is missing some supports, and it's relatively not easy to turn our benchmarks into SQL queries, we plan to add a new tool like "secondary-bench" to benchmark the performance and verify our storage engine's correctness in a large dataset. It may be very similar to RocksDB's db_bench tool, with the following functionality:

• secondary-bench filltable <table name> <schema>
• secondary-bench scan <table name> <column>
• secondary-bench sort-scan <table name> <column>
• secondary-bench compact <table name>
• etc.