pgsql: Add more columns to pg_stat_ssl

Add more columns to pg_stat_ssl

Add columns client_serial and issuer_dn to pg_stat_ssl.  These allow
uniquely identifying the client certificate.

Rename the existing column clientdn to client_dn, to make the naming
more consistent and easier to read.

Discussion: https://www.postgresql.org/message-id/flat/398754d8-6bb5-c5cf-e7b8-22e5f0983caf@2ndquadrant.com/

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f60a0e96778854ed0b7fd4737488ba88022e47bd

Modified Files
--------------
doc/src/sgml/monitoring.sgml          | 20 ++++++++++++++++++--
src/backend/catalog/system_views.sql  |  4 +++-
src/backend/libpq/be-secure-openssl.c | 31 ++++++++++++++++++++++++++++++-
src/backend/postmaster/pgstat.c       |  4 +++-
src/backend/utils/adt/pgstatfuncs.c   | 22 ++++++++++++++++++----
src/include/catalog/catversion.h      |  2 +-
src/include/catalog/pg_proc.dat       |  6 +++---
src/include/libpq/libpq-be.h          |  4 +++-
src/include/pgstat.h                  | 16 +++++++++++++---
src/test/regress/expected/rules.out   | 10 ++++++----
src/test/ssl/t/001_ssltests.pl        |  8 ++++----
11 files changed, 102 insertions(+), 25 deletions(-)