Avoids having replicate on write tasks stacking up at CL.ONE

The counter design involves a read on the first replica during a write. At CL.ONE, this read is not involved in the latency of the operation (the write is acknowledged before). This means it is fairly easy to insert too quickly at CL.ONE and have the replicate on write tasks falling behind. The goal of this ticket is to protect against that.

An option could be to bound the replicate on write task queue so that write start to block once we have too much of those in the queue. Another option could be to drop the oldest tasks when they are too old, but it's probably a more unsafe option.