GSS information (if used) such as if the connection was authorized using
GSS or if it was encrypted using GSS, and perhaps most importantly, what
the GSS principal used for the authentication was, is extremely useful
but wasn't being included in the connection authorized log message.

Therefore, add to the connection authorized log message that
information, in a similar manner to how we log SSL information when SSL
is used for a connection.

Author: Vignesh C
Reviewed-by: Bharath Rupireddy
Discussion: https://www.postgresql.org/message-id/CALDaNm2N1385_Ltoo%3DS7VGT-ESu_bRQa-sC1wg6ikrM2L2Z49w%40mail.gmail.com