pgsql: Support for SSSSS datetime format pattern

Support for SSSSS datetime format pattern

SQL Standard 2016 defines SSSSS format pattern for seconds past midnight in
jsonpath .datetime() method and CAST (... FORMAT ...) SQL clause.  In our
datetime parsing engine we currently support it with SSSS name.

This commit adds SSSSS as an alias for SSSS.  Alias is added in favor of
upcoming jsonpath .datetime() method.  But it's also supported in to_date()/
to_timestamp() as positive side effect.

Discussion: https://postgr.es/m/CAPpHfdsZgYEra_PeCLGNoXOWYx6iU-S3wF8aX0ObQUcZU%2B4XTw%40mail.gmail.com
Author: Nikita Glukhov, Alexander Korotkov
Reviewed-by: Anastasia Lubennikova, Peter Eisentraut

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/b64b857f50fb51da1588c54a56f8fc1c0d491058

Modified Files
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doc/src/sgml/func.sgml                 |  2 +-
src/backend/utils/adt/formatting.c     | 12 ++++++++----
src/test/regress/expected/horology.out | 20 ++++++++++++++++++++
src/test/regress/sql/horology.sql      |  4 ++++
4 files changed, 33 insertions(+), 5 deletions(-)