Ability to limit throughput in bytes per second

[adutra]

This came as a follow-up to #435: we currently have the ability to limit throughput in ops/second, but we don't have the ability to limit it in bytes/sec.

And yet all the required bits are present: we already have a DataSizes class that is used to track statement and row sizes in two situations: when batching by data size, and when reporting rates in bytes/sec.

┆Issue is synchronized with this Jira Task by Unito