pgsql: doc: Fix some grammar for logical decoding description and funct

doc: Fix some grammar for logical decoding description and functions

This documentation is has been added for the support of logical decoding
on standbys.  Some markups were missing, hence add some where required.

Author: Thom Brown
Reviewed-by: Justin Pryzby, Daniel Gustafsson
Discussion: https://postgr.es/m/CAA-aLv7xCZ0nBJa-NWe0rxBB28TjFjS2JtjiZMoQ+0wsugG+hQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c7dc56bd6b36b4d6b3c6cc1bb4735f7777272ca3

Modified Files
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doc/src/sgml/func.sgml            |  4 ++--
doc/src/sgml/logicaldecoding.sgml | 22 ++++++++++++----------
doc/src/sgml/monitoring.sgml      |  2 +-
3 files changed, 15 insertions(+), 13 deletions(-)