PostgreSQL gen_random_uuid polyfill for <13

gen_random_uuid_polyfill.sql

DO $_$
BEGIN
IF NOT EXISTS (SELECT 1 FROM pg_proc WHERE proname = 'gen_random_uuid') THEN
	CREATE EXTENSION IF NOT EXISTS "uuid-ossp";
	CREATE FUNCTION gen_random_uuid()	
	RETURNS uuid
	LANGUAGE sql
	AS $$
	SELECT uuid_generate_v4()
	$$;
END IF;
END
$_$;