pgsql: doc PG 18 relnotes: add GROUP BY column elimination item

doc PG 18 relnotes: add GROUP BY column elimination item

With a nod to PG 9.6.

Reported-by: jian he

Discussion: /messages/by-id/CACJufxEqs=EXZETwtaOooTFhZrtxvSWg8M2uPfzjNtS3wQ6Dzw@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/24987c6f0687576da97b593c6dd5740ccdd23277

Modified Files
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doc/src/sgml/release-18.sgml | 17 +++++++++++++++++
1 file changed, 17 insertions(+)