Read your own writes

[zknill]

Currently the writes are forwarded to the upstream postgres server, the write request as processed by SQLedge can return before the data is received back to SQLedge on the replication connection. This breaks the read-your-own-writes property.

Implement a feature/config that allows proxied writes to wait for the written data to be received back from the replication protocol before returning.

This could probably be off by default, as it will introduce more latency than the write alone (as we wait to received the write back).