Praefect: Enable Postgres binary protocol

PgBouncer limits usage of placeholders in queries, because it prepares statement first and execute it afterwards. The problem could be if statement will be prepared using one session, but executed using another session. Binary format will issue only single operation without preparing statement.

Part of: #2166 (closed)

It is required to represent []byte as string type because of https://github.com/lib/pq/issues/528.
Enabled binary format https://godoc.org/github.com/lib/pq#hdr-Data_Types.
PgBouncer restriction: https://www.pgbouncer.org/faq.html#how-to-use-prepared-statements-with-transaction-pooling