Evaluate the performant restore's speed limit

[xumengpanda]

The performant restore (aka fast restore) performance can be limited by the destination FDB cluster's write throughput.

To better understand the impact of the FDB cluster's write throughput on the restore system's performance, we can let the restore system simulate the write-to-DB operation instead of actually writing to the DB. We can tune the simulated write-latency (and throughput) to understand the performance limit of the performant restore.