Add a test for prepared CALL

it requires pytest, and the purpose is to test when param is the
distribution key

src/test/regress/citus_tests/test/test_prepared_statements.py

@@ -0,0 +1,31 @@
+import psycopg
+import pytest
+
+def test_call_param(cluster):
+    # create a distributed table and an associated distributed procedure
+    # to ensure parameterized CALL succeed, even when the param is the
+    # distribution key.
+    coord = cluster.coordinator
+    coord.sql("CREATE TABLE test(i int)")
+    coord.sql(
+        """
+        CREATE PROCEDURE p(_i INT) LANGUAGE plpgsql AS $$
+        BEGIN
+        INSERT INTO test(i) VALUES (_i);
+        END; $$
+        """
+    )
+    sql = "CALL p(%s)"
+
+    # prepare/exec before distributing
+    coord.sql_prepared(sql, (1,))
+
+    coord.sql("SELECT create_distributed_table('test', 'i')")
+    coord.sql("SELECT create_distributed_function('p(int)', distribution_arg_name := '_i', colocate_with := 'test')")
+
+    # prepare/exec after distribution
+    coord.sql_prepared(sql, (2,))
+
+    sum_i = coord.sql_value("select sum(i) from test;")
+
+    assert sum_i == 3