Add TAP tests for LDAP connection parameter lookup

Add TAP tests for LDAP connection parameter lookup

Add TAP tests that tests the LDAP Lookup of Connection Parameters
functionality in libpq.  Prior to this commit, LDAP test coverage only
existed for the server-side authentication functionality and for
connection service file with parameters directly specified in the
file.  The tests included here test a pg_service.conf that contains a
link to an LDAP system that contains all of the connection parameters.

Author: Andrew Jackson <andrewjackson947@gmail.com>
Discussion: https://www.postgresql.org/message-id/CAKK5BkHixcivSCA9pfd_eUp7wkLRhvQ6OtGLAYrWC%3Dk7E76LDQ%40mail.gmail.com