[YSQL] Test fk-contention in isolation regress suite fails (the test hasn't yet been added)

[pkj415]

Jira Link: DB-496

Description

Check fk-contention.spec for the test and fk-contention.out for the expected output. We fail in YSQL because the UPDATE conflicts with the lock taken by the INSERT. Avoiding the conflict will help us improve performance in such cases and also achieve same semantics as Pg.

To quickly repro it, add "test: fk-contention" to the yb_pg_isolation_schedule, comment out other tests and then run either -

1. To run against locally running cluster, inside yugabyte-db repo:

> mkdir -p pgregress_output/yb_pg_isolation_schedule

> YB_PG_REGRESS_RESULTSFILE_POSTPROCESS_CMD=`pwd`/python/yugabyte/pg_regress_postprocess_output.py ./build/latest/postgres_build/src/test/isolation/pg_isolation_regress --bindir=./build/latest/postgres/bin --use-existing --inputdir=./src/postgres/src/test/isolation --outputdir=./pgregress_output/yb_pg_isolation_schedule --schedule=./src/postgres/src/test/isolation/yb_pg_isolation_schedule --host=127.0.0.1 --port=5433 --user=yugabyte --dbname=yugabyte

2. Via java test (slower): ./yb_build.sh --java-test org.yb.pgsql.TestPgIsolationRegress#isolationRegress