pgsql: Allow custom search filters to be configured for LDAP auth

Allow custom search filters to be configured for LDAP auth

Before, only filters of the form "(<ldapsearchattribute>=<user>)"
could be used to search an LDAP server. Introduce ldapsearchfilter
so that more general filters can be configured using patterns, like
"(|(uid=$username)(mail=$username))" and "(&(uid=$username)
(objectClass=posixAccount))". Also allow search filters to be included
in an LDAP URL.

Author: Thomas Munro
Reviewed-By: Peter Eisentraut, Mark Cave-Ayland, Magnus Hagander
Discussion: https://postgr.es/m/CAEepm=0XTkYvMci0WRubZcf_1am8=gP=7oJErpsUfRYcKF2gwg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/83aaac41c66959a3ebaec7daadc4885b5f98f561

Modified Files
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doc/src/sgml/client-auth.sgml | 43 +++++++++++++++++++++++++++++++++++----
src/backend/libpq/auth.c | 44 ++++++++++++++++++++++++++++++++--------
src/backend/libpq/hba.c | 47 +++++++++++++++++++++++++++++++------------
src/include/libpq/hba.h | 1 +
4 files changed, 110 insertions(+), 25 deletions(-)