Add charts submodule and test-kong-chart.sh script for regression test

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "hack/test/charts"]
+	path = hack/test/charts
+	url = https://github.com/Kong/charts

hack/test/test-kong-chart.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# Update submodule to the latest commit
+git submodule update --init --recursive
+
+# Loop through each directory in charts/charts and run helm dependency update
+for dir in charts/charts/*; do
+    if [ -d "$dir" ]; then
+        cd "$dir"
+        helm dependency update
+        cd -
+    fi
+done
+
+# Run make test.golden and check return code
+make -C charts/ test.golden
+if [ $? -eq 0 ]; then
+    echo "Tests passed successfully."; exit 0
+else
+    echo "Tests failed."; exit 1
+fi