catch non default GUCs in execution context, impacting execution plan

[legrandlegrand]

see
https://www.postgresql-archive.org/explain-plans-with-information-about-modified-gucs-td6062825.html

[legrandlegrand]

after applying
explain-with-gucs-v3.patch

changing pg_stat_sql_plans.c
with
+ es->gucs = true;
es->format = EXPLAIN_FORMAT_TEXT;

returns non default performance gucs in logs with explain

[legrandlegrand]

in pg12, this has been renamed from explain (GUCS ON) to explain (SETTINGS ON)
see https://git.postgresql.org/pg/commitdiff/ea569d64ac7174d3fe657e3e682d11053ecf1866