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