pgsql: doc: Update SQL keywords list to SQL:2023

doc: Update SQL keywords list to SQL:2023

Per previous convention (see
ace397e9d24eddc56e7dffa921f506117b602d78), drop SQL:2011 and only keep
the latest two standards and SQL-92.

Discussion: https://www.postgresql.org/message-id/flat/63f285d9-4ec8-0c9e-4bf5-e76334ddc0af@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1993f3feb74f30e71c4139ace66ccc1e0225b4a8

Modified Files
--------------
doc/src/sgml/generate-keywords-table.pl            |  2 +-
...-nonreserved.txt => sql2023-02-nonreserved.txt} | 38 +++++++++++++++
...011-02-reserved.txt => sql2023-02-reserved.txt} | 56 +++++++++++++++++++++-
...-nonreserved.txt => sql2023-09-nonreserved.txt} |  0
...011-09-reserved.txt => sql2023-09-reserved.txt} |  4 +-
...-nonreserved.txt => sql2023-14-nonreserved.txt} |  6 +--
...011-14-reserved.txt => sql2023-14-reserved.txt} |  0
7 files changed, 96 insertions(+), 10 deletions(-)