pgsql: Add pg_stat_wal statistics view.

Add pg_stat_wal statistics view.

This view shows the statistics about WAL activity. Currently it has only
two columns: wal_buffers_full and stats_reset. wal_buffers_full column
indicates the number of times WAL data was written to the disk because
WAL buffers got full. This information is useful when tuning wal_buffers.
stats_reset column indicates the time at which these statistics were
last reset.

pg_stat_wal view is also the basic infrastructure to expose other
various statistics about WAL activity later.

Bump PGSTAT_FILE_FORMAT_ID due to the change in pgstat format.

Bump catalog version.

Author: Masahiro Ikeda
Reviewed-by: Takayuki Tsunakawa, Kyotaro Horiguchi, Amit Kapila, Fujii Masao
Discussion: https://postgr.es/m/188bd3f2d2233cf97753b5ced02bb050@oss.nttdata.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8d9a935965f01b7759a8c23ff6291000b670a2bf

Modified Files
--------------
doc/src/sgml/monitoring.sgml           |  63 ++++++++++++++++-
src/backend/access/transam/xlog.c      |   1 +
src/backend/catalog/system_views.sql   |   6 ++
src/backend/postmaster/checkpointer.c  |   3 +
src/backend/postmaster/pgstat.c        | 120 +++++++++++++++++++++++++++++++--
src/backend/utils/adt/pgstatfuncs.c    |  36 ++++++++++
src/include/catalog/catversion.h       |   2 +-
src/include/catalog/pg_proc.dat        |   8 +++
src/include/pgstat.h                   |  33 ++++++++-
src/test/regress/expected/rules.out    |   3 +
src/test/regress/expected/sysviews.out |   7 ++
src/test/regress/sql/sysviews.sql      |   3 +
src/tools/pgindent/typedefs.list       |   2 +
13 files changed, 276 insertions(+), 11 deletions(-)