Chart: Make controller.config templatable. (#11181)

* [helm] pass controller.config through tpl

* add unittest

* update README.md

* Update charts/ingress-nginx/README.md

Co-authored-by: Marco Ebert <marco_ebert@icloud.com>

* Update charts/ingress-nginx/tests/controller-configmap_test.yaml

Co-authored-by: Marco Ebert <marco_ebert@icloud.com>

* Update charts/ingress-nginx/values.yaml

Co-authored-by: Marco Ebert <marco_ebert@icloud.com>

---------

Co-authored-by: Marco Ebert <marco_ebert@icloud.com>

charts/ingress-nginx/tests/controller-configmap_test.yaml

@@ -12,3 +12,20 @@ tests:
       - equal:
           path: metadata.name
           value: RELEASE-NAME-ingress-nginx-controller
+
+  - it: should create a ConfigMap with templated values if `controller.config` contains templates
+    set:
+      controller.config:
+        global-rate-limit-memcached-host: "memcached.{{ .Release.Namespace }}.svc.kubernetes.local"
+        global-rate-limit-memcached-port: 11211
+        use-gzip: true
+    asserts:
+      - equal:
+          path: data.global-rate-limit-memcached-host
+          value: memcached.NAMESPACE.svc.kubernetes.local
+      - equal:
+          path: data.global-rate-limit-memcached-port
+          value: "11211"
+      - equal:
+          path: data.use-gzip
+          value: "true"