pgsql: pg_upgrade doc: mention that replication slots must be recreated

pg_upgrade doc: mention that replication slots must be recreated

Reported-by: Nikhil Shetty

Discussion: /messages/by-id/CAFpL5Vxastip0Jei-K-=7cKXTg=5sahSe5g=om=x68NOX8+PUA@mail.gmail.com

Backpatch-through: 10

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/e24ea2a97f059aece02925def9889351a3ac3110

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