Evaluate lesser joins to produce best join tree
Evaluate lesser joins to produce best join tree

Previously we were setting the value of
`optimizer_join_arity_for_associativity_commutativity` to very large
number and so ORCA would spend a very long time evaluating all possible n_way_join
combinations to come up with the cheapest join tree to use in the plan.

We are reducing this value to `7` as it does not prove to be beneficial
to spend time and resources to evaluate any more than 7_way_joins in
trying to find the cheapest join tree.

greenplum-db/gpdb,xinzweb/gpdb,janebeckman/gpdb,Chibin/gpdb,edespino/gpdb,janebeckman/gpdb,Chibin/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,Chibin/gpdb,lisakowen/gpdb,janebeckman/gpdb,jmcatamney/gpdb,50wu/gpdb,Chibin/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,Chibin/gpdb,Chibin/gpdb,edespino/gpdb,yuanzhao/gpdb,edespino/gpdb,jmcatamney/gpdb,50wu/gpdb,adam8157/gpdb,yuanzhao/gpdb,janebeckman/gpdb,adam8157/gpdb,ashwinstar/gpdb,janebeckman/gpdb,xinzweb/gpdb,xinzweb/gpdb,edespino/gpdb,jmcatamney/gpdb,janebeckman/gpdb,jmcatamney/gpdb,adam8157/gpdb,lisakowen/gpdb,edespino/gpdb,janebeckman/gpdb,xinzweb/gpdb,lisakowen/gpdb,janebeckman/gpdb,ashwinstar/gpdb,adam8157/gpdb,ashwinstar/gpdb,adam8157/gpdb,greenplum-db/gpdb,Chibin/gpdb,ashwinstar/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,yuanzhao/gpdb,edespino/gpdb,xinzweb/gpdb,edespino/gpdb,ashwinstar/gpdb,50wu/gpdb,greenplum-db/gpdb,50wu/gpdb,Chibin/gpdb,edespino/gpdb,ashwinstar/gpdb,50wu/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,Chibin/gpdb,xinzweb/gpdb,xinzweb/gpdb,jmcatamney/gpdb,lisakowen/gpdb,lisakowen/gpdb,janebeckman/gpdb,lisakowen/gpdb,yuanzhao/gpdb,ashwinstar/gpdb,edespino/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,adam8157/gpdb,yuanzhao/gpdb,janebeckman/gpdb,adam8157/gpdb,greenplum-db/gpdb,Chibin/gpdb,yuanzhao/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,yuanzhao/gpdb,lisakowen/gpdb,adam8157/gpdb,ashwinstar/gpdb,50wu/gpdb,edespino/gpdb