pgsql: doc: Correct the description about the length of pg_stat_activit

doc: Correct the description about the length of pg_stat_activity.query.

pg_stat_activity.query text is truncated at 1024 bytes. But previously
the document described that it's truncated at 1024 characters.
This was not accurate when considering multibyte characters.

Back-patch to v10 where this inaccurate description was added.

Author: Atsushi Torikoshi
Reviewed-by: Daniel Gustafsson, Fujii Masao
Discussion: https://postgr.es/m/cd5b49a5a14e887542f5f569c1c6bde2@oss.nttdata.com

Branch
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REL_10_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/f03a34ad2cf3e17fe9b3aef53e97e0fae60a3a20

Modified Files
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doc/src/sgml/monitoring.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)