pgsql: doc: Fix description of replication command CREATE_REPLICATION_S

doc: Fix description of replication command CREATE_REPLICATION_SLOT

The output plugin name is a mandatory option when creating a logical
slot, but the grammar documented was not described as such. While on
it, fix two comments in repl_gram.y to show that TEMPORARY is an
optional grammar choice.

Author: Ayaki Tachikake
Discussion: /messages/by-id/OSAPR01MB2852607B2329FFA27834105AF1229@OSAPR01MB2852.jpnprd01.prod.outlook.com
Backpatch-through: 15

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/91416f45f8bb8c4466e577efd79822be11645794

Modified Files
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doc/src/sgml/protocol.sgml | 2 +-
src/backend/replication/repl_gram.y | 4 ++--
2 files changed, 3 insertions(+), 3 deletions(-)