[YSQL] Tuning parameters for faster copy performance.

[lnguyen-yugabyte]

Jira Link: DB-1977

Description

Adjust the default among the following parameters for optimal copy performance:
`

• ROWS_PER_TRANSACTION
• ysql_session_max_batch_size
• ysql_max_in_flight_ops
  `

Make sure to report the result of the copy performance via microbenchmarking through the cloud cluster.