pgsql: Add stats_reset column to pg_stat_database_conflicts.

Add stats_reset column to pg_stat_database_conflicts.

This commit adds a stats_reset column to pg_stat_database_conflicts,
allowing users to see when the statistics in this view were last reset.
This makes the view consistent with pg_stat_database and other statistics
views.

Catalog version bumped.

Author: Shihao Zhong <zhong950419(at)gmail(dot)com>
Reviewed-by: Sami Imseih <samimseih(at)gmail(dot)com>
Reviewed-by: Kirill Reshke <reshkekirill(at)gmail(dot)com>
Reviewed-by: Chao Li <li(dot)evan(dot)chao(at)gmail(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAGRkXqS98OebEWjax99_LVAECsxCB8i=BfsdAL34i-5QHfwyOQ@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/723619eaa3a85f32ce8c2d32c063da26f89ca8d2

Modified Files
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doc/src/sgml/monitoring.sgml | 9 +++++++++
src/backend/catalog/system_views.sql | 3 ++-
src/include/catalog/catversion.h | 2 +-
src/test/regress/expected/rules.out | 3 ++-
src/test/regress/expected/stats.out | 19 +++++++++++++++++--
src/test/regress/sql/stats.sql | 9 +++++++--
6 files changed, 38 insertions(+), 7 deletions(-)