pgsql: doc PG 17 relnotes: clarify pg_upgrade and logical slot preserv.

doc PG 17 relnotes: clarify pg_upgrade and logical slot preserv.

Reported-by: Amit Kapila

Discussion: /messages/by-id/CAA4eK1+bChgccySmcm0LbvkmBDJ3ufsLneF4iNa_aZ7t2P6=8w@mail.gmail.com

Backpatch-through: 17 only

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/912d15cba50c257f2195f79d3f80bad26996c018

Modified Files
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doc/src/sgml/release-17.sgml | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)