chore: enable dependabot for gateway addons helm chart (#7758)

add gateway addons helm to dependabot

Signed-off-by: Huabing Zhao <zhaohuabing@gmail.com>

Author: zhaohuabing

.github/dependabot.yml

@@ -70,3 +70,8 @@ updates:
       - /tools/src/yamllint
     schedule:
       interval: weekly
+  - package-ecosystem: "helm"
+    directories:
+      - "/charts/gateway-addons-helm"
+    schedule:
+      interval: "weekly"