pgsql: Show shared object statistics in pg_stat_database

Show shared object statistics in pg_stat_database

This adds a row to the pg_stat_database view with datoid 0 and datname
NULL for those objects that are not in a database. This was added
particularly for checksums, but we were already tracking more satistics
for these objects, just not returning it.

Also add a checksum_last_failure column that holds the timestamptz of
the last checksum failure that occurred in a database (or in a
non-dataabase file), if any.

Author: Julien Rouhaud <rjuju123(at)gmail(dot)com>

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/77bd49adba4711b4497e7e39a5ec3a9812cbd52a

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 26 ++++++++++++++++++--------
doc/src/sgml/ref/initdb.sgml | 4 +++-
doc/src/sgml/ref/pg_basebackup.sgml | 3 ++-
src/backend/catalog/system_views.sql | 12 ++++++++++--
src/backend/postmaster/pgstat.c | 6 +++++-
src/backend/replication/basebackup.c | 4 ++--
src/backend/utils/adt/pgstatfuncs.c | 18 ++++++++++++++++++
src/include/catalog/pg_proc.dat | 5 +++++
src/include/pgstat.h | 2 ++
src/test/regress/expected/rules.out | 13 +++++++++++--
10 files changed, 76 insertions(+), 17 deletions(-)