pgsql: doc: Recommend pg_stat_io rather than pg_stat_wal in WAL configu

doc: Recommend pg_stat_io rather than pg_stat_wal in WAL configuration

Since a051e71e28a1, pg_stat_io is able to track statistics for the WAL
activity, providing an equivalent of pg_stat_wal with more granularity
for the fsyncs/writes counts and timings, as the data is split across
backend types.

This commit now recommends pg_stat_io rather than pg_stat_wal in the
section "WAL configuration", some of the latter's attributes being
candidate for removal in a follow-up commit.

Extracted from a larger patch by the same author.

Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Discussion: https://postgr.es/m/Z7RkQ0EfYaqqjgz/@ip-10-97-1-34.eu-west-3.compute.internal

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/2f70871c2bc18d103d5dd25ff9d91e0da29412ee

Modified Files
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doc/src/sgml/wal.sgml | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)