Adds the option for clear text password authentication.

Fixes connections to Azure Database for PostgreSQL.

I created a new boolean parameter at the time of creating the connection called allowClearTextPassword default to false to enable this kind of authentication for the connection.

According to https://www.postgresql.org/docs/11/protocol-flow.html#id-1.10.5.7.3 flow, this patch just returns the password to the server when requested a clear text password after a connection attempt.

For the structure of the message I didn't quite got the grasp of the byte formatting, but replicated the structure used for md5 as it follows a similar message flow. Need review on this to guarantee it is working. Local testing showed no problem.

TODO 1: I could not come up with tests, as there should be a SQL server running with clear text password request configuration I cannot replicate. Please advise on whether such server exists or how could I write the necessary tests. I have successfully tested the changes under our environment, for both queries and transactions of every type.

TODO 2: There may be security concerns about using clear text passwords I am not aware of. Right now we have an open ticket with Microsoft regarding this issue. Note that in this environment, the connections are performed within a private cloud cluster and encrypted, thus making the password encryption non necessary.