pgsql: Add wal_fpi_bytes to pg_stat_wal and pg_stat_get_backend_wal()

Add wal_fpi_bytes to pg_stat_wal and pg_stat_get_backend_wal()

This new counter, called "wal_fpi_bytes", tracks the total amount in
bytes of full page images (FPIs) generated in WAL. This data becomes
available globally via pg_stat_wal, and for backend statistics via
pg_stat_get_backend_wal().

Previously, this information could only be retrieved with pg_waldump or
pg_walinspect, which may not be available depending on the environment,
and are expensive to execute. It offers hints about how much FPIs
impact the WAL generated, which could be a large percentage for some
workloads, as well as the effects of wal_compression or page holes.

Bump catalog version.
Bump PGSTAT_FILE_FORMAT_ID, due to the addition of wal_fpi_bytes in
PgStat_WalCounters.

Author: Shinya Kato <shinya11(dot)kato(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Discussion: https://postgr.es/m/CAOzEurQtZEAfg6P0kU3Wa-f9BWQOi0RzJEMPN56wNTOmJLmfaQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/f9a09aa2952039a9956b44d929b9df74d62a4cd4

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 9 +++++++++
src/backend/access/transam/xloginsert.c | 6 ++++++
src/backend/catalog/system_views.sql | 1 +
src/backend/executor/instrument.c | 2 ++
src/backend/utils/activity/pgstat_backend.c | 1 +
src/backend/utils/activity/pgstat_wal.c | 1 +
src/backend/utils/adt/pgstatfuncs.c | 20 ++++++++++++++------
src/include/catalog/catversion.h | 2 +-
src/include/catalog/pg_proc.dat | 12 ++++++------
src/include/executor/instrument.h | 1 +
src/include/pgstat.h | 3 ++-
src/test/regress/expected/rules.out | 3 ++-
12 files changed, 46 insertions(+), 15 deletions(-)