pgsql: ssl: Add tests for client CA

ssl: Add tests for client CA

These tests were originally written to test the SSL SNI patchset
but they have merit on their own since we lack coverage for these
scenarios in the non SNI case as well.

Author: Jacob Champion <jacob.champion@enterprisedb.com>
Co-authored-by: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/1C81CD0D-407E-44F9-833A-DD0331C202E5@yesql.se

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/25e568ba7ce712c41acf7058ef14dd49d912c3ab

Modified Files
--------------
src/test/ssl/t/001_ssltests.pl        | 56 +++++++++++++++++++++++++++++++++++
src/test/ssl/t/SSL/Backend/OpenSSL.pm | 16 ++++++++--
2 files changed, 69 insertions(+), 3 deletions(-)