Add end-to-end test for JOIN...USING syntax

PostgreSQL test case validating JOIN USING feature works
correctly with existing database engines.

Author: mgilbir

internal/endtoend/testdata/join_using_single/postgresql/go/db.go

@@ -0,0 +1,4 @@
+-- name: GetOrdersWithShipments :many
+SELECT *
+FROM orders
+LEFT JOIN shipments USING (order_id);

internal/endtoend/testdata/join_using_single/postgresql/go/models.go

@@ -0,0 +1,11 @@
+CREATE TABLE orders (
+    order_id SERIAL PRIMARY KEY,
+    customer_name TEXT,
+    amount DECIMAL(10, 2)
+);
+
+CREATE TABLE shipments (
+    shipment_id SERIAL PRIMARY KEY,
+    order_id INT REFERENCES orders(order_id),
+    address TEXT
+);

internal/endtoend/testdata/join_using_single/postgresql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "postgresql/go",
+      "engine": "postgresql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}