pgsql: Add PROCESS_MAIN to VACUUM

Add PROCESS_MAIN to VACUUM

Disabling this option is useful to run VACUUM (with or without FULL) on
only the toast table of a relation, bypassing the main relation.  This
option is enabled by default.

Running directly VACUUM on a toast table was already possible without
this feature, by using the non-deterministic name of a toast relation
(as of pg_toast.pg_toast_N, where N would be the OID of the parent
relation) in the VACUUM command, and it required a scan of pg_class to
know the name of the toast table.  So this feature is basically a
shortcut to be able to run VACUUM or VACUUM FULL on a toast relation,
using only the name of the parent relation.

A new switch called --no-process-main is added to vacuumdb, to work as
an equivalent of PROCESS_MAIN.

Regression tests are added to cover VACUUM and VACUUM FULL, looking at
pg_stat_all_tables.vacuum_count to see how many vacuums have run on
each table, main or toast.

Author: Nathan Bossart
Reviewed-by: Masahiko Sawada
Discussion: https://postgr.es/m/20221230000028.GA435655@nathanxps13

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4211fbd8413b26e0abedbe4338aa7cda2cd469b4

Modified Files
--------------
doc/src/sgml/ref/vacuum.sgml         | 13 +++++++++++
doc/src/sgml/ref/vacuumdb.sgml       | 15 ++++++++++++
src/backend/commands/vacuum.c        | 28 ++++++++++++++++++-----
src/backend/postmaster/autovacuum.c  |  4 +++-
src/bin/psql/tab-complete.c          |  4 ++--
src/bin/scripts/t/100_vacuumdb.pl    |  7 ++++++
src/bin/scripts/vacuumdb.c           | 24 ++++++++++++++++++++
src/include/commands/vacuum.h        |  9 ++++----
src/test/regress/expected/vacuum.out | 44 +++++++++++++++++++++++++++++++++++-
src/test/regress/sql/vacuum.sql      | 23 ++++++++++++++++++-
10 files changed, 156 insertions(+), 15 deletions(-)