doc: Clarify that total_vacuum_time excludes VACUUM FULL.

doc: Clarify that total_vacuum_time excludes VACUUM FULL.

The last_vacuum and vacuum_count fields in pg_stat_all_tables already
state that they do not include VACUUM FULL. However, total_vacuum_time,
which also excludes VACUUM FULL, did not mention this. This could
mislead users into thinking VACUUM FULL time is included.

To address this, this commit updates the documentation for
pg_stat_all_tables to explicitly state that total_vacuum_time does not
count VACUUM FULL.

Back-patched to v18, where total_vacuum_time was introduced.

Additionally, this commit clarifies that n_ins_since_vacuum also
excludes VACUUM FULL. Although n_ins_since_vacuum was added in v13,
we are not back-patching this change to stable branches, as it is
a documentation improvement, not a bug fix.

Author: Fujii Masao <masao.fujii@gmail.com>
Reviewed-by: Robert Treat <rob@xzilla.net>
Reviewed-by: David G. Johnston <david.g.johnston@gmail.com>
Reviewed-by: Laurenz Albe <laurenz.albe@cybertec.at>
Discussion: https://postgr.es/m/2ac375d1-591b-4f1b-a2af-f24335567866@oss.nttdata.com
Backpatch-through: 18