pgsql: Avoid instabilities with the regression tests of pg_freespacemap

Avoid instabilities with the regression tests of pg_freespacemap

It was possible to run those tests with installcheck, but they are
actually unstable as concurrent autovacuum jobs could prevent the
truncation of the filespace map to happen (aka the scan of pg_database
when building the list of relations to clean), an assumption we rely on
when checking that the FSM of the relation gets truncated during a
manual vacuum after deleting all the relation's data.

This commit adds a NO_INSTALLCHECK to disallow installcheck, and
introduces the use of a custom configuration file with autovacuum
disabled.

It happens that we already do that in the recovery test
008_fsm_truncation, for example.

Reported-by: Tom Lane, via buildfarm member skink
Discussion: https://postgr.es/m/381910.1648401526@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c14a9eeec4797358922f8696d76716501b86c57d

Modified Files
--------------
contrib/pg_freespacemap/Makefile             | 5 +++++
contrib/pg_freespacemap/pg_freespacemap.conf | 1 +
2 files changed, 6 insertions(+)