R2DBC deferred connection creation

[pboklashov]

Description

According to R2DBC specification, ConnectionFactory implementation must deffer connection creation (https://r2dbc.io/spec/1.0.0.RELEASE/spec/html/#connections.factory). ClickHouseConnectionFactory created connection when ClickHouseConnectionFactory#create is called.

Therefore tools that rely on deferred connection creation (for instance, r2dbc-pool) always gets the same connection instance, close all instances at once, and then get only already closed connections from ClickHouseConnectionFactory#create.

Steps to reproduce

1. Create several connection using Mono created by ClickHouseConnectionFactory#create
2. Observe that instance of Connection is always the same

Expected behaviour

Mono, returned by ClickHouseConnectionFactory, creates new instance of Connection on each subscription.

Configuration

Environment

• Client version: 0.4.6

[chernser]

Fix merged