Track skipped tables during autovacuum and autoanalyze

Hi,

I would like to propose adding new fields to pg_stat_all_tables to track
tables skipped during autovacuum and autoanalyze.

Currently, when autovacuum or autoanalyze is skipped because a lock cannot
be acquired, this information is only emitted in log messages. However, it
would be more useful if users could access this information via a system view,
alongside related fields such as last_autovacuum, on a per-table basis.

The attached patch add the following fields to pg_stat_all_tables:
- last_skipped_autovacuum
- last_skipped_autoanalyze
- skipped_autovacuum_count
- skipped_autoanalyze_count

Are there any concerns about exposing this in pg_stat_all_tables, or suggestions
for a better approach?

Regards,
Yugo Nagata

--
Yugo Nagata <nagata(at)sraoss(dot)co(dot)jp>