pgsql: Support configuring TLSv1.3 cipher suites

Support configuring TLSv1.3 cipher suites

The ssl_ciphers GUC can only set cipher suites for TLSv1.2, and lower,
connections. For TLSv1.3 connections a different OpenSSL API must be
used.  This adds a new GUC, ssl_tls13_ciphers, which can be used to
configure a colon separated list of cipher suites to support when
performing a TLSv1.3 handshake.

Original patch by Erica Zhang with additional hacking by me.

Author: Erica Zhang <ericazhangy2021@qq.com>
Author: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Jacob Champion <jacob.champion@enterprisedb.com>
Reviewed-by: Andres Freund <andres@anarazel.de>
Reviewed-by: Peter Eisentraut <peter@eisentraut.org>
Reviewed-by: Jelte Fennema-Nio <postgres@jeltef.nl>
Discussion: https://postgr.es/m/tencent_063F89FA72CCF2E48A0DF5338841988E9809@qq.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/45188c2ea2391b7b24039e1632c726e2fc6b8008

Modified Files
--------------
doc/src/sgml/config.sgml                      | 36 +++++++++++++++++++++------
src/backend/libpq/be-secure-openssl.c         | 22 +++++++++++++---
src/backend/libpq/be-secure.c                 |  1 +
src/backend/utils/misc/guc_tables.c           | 15 +++++++++--
src/backend/utils/misc/postgresql.conf.sample |  3 ++-
src/include/libpq/libpq.h                     |  1 +
src/test/ssl/t/SSL/Server.pm                  |  3 ++-
7 files changed, 66 insertions(+), 15 deletions(-)