pgsql: doc: add SSL configuration section reference

doc: add SSL configuration section reference

Reported-by: Steve Atkins

Discussion: /messages/by-id/B82E80DD-1452-4175-B19C-564FE46705BA@blighty.com

Backpatch-through: 11

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/61fcc9d440cb85a6799fa309ef9c61e658215a11

Modified Files
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doc/src/sgml/client-auth.sgml | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)