Reference NGINX Ingress Controller v1.2.1

References version 1.2.1 of the NGINX Ingress Controller, mirrored in
gitlab-org/cloud-native/mirror/images!6.

Digest was collected via:

```
$ skopeo inspect docker://k8s.gcr.io/ingress-nginx/controller:v1.2.1 | jq -r '.Digest'
sha256:5516d103a9c2ecc4f026efbd4b40662ce22dc1f824fb129ed121460aaa5c47f8
```

Closes #3403

Changelog: changed

charts/nginx-ingress/values.yaml

@@ -12,8 +12,8 @@ controller:
   image:
     registry: k8s.gcr.io
     repository: registry.gitlab.com/gitlab-org/cloud-native/mirror/images/ingress-nginx/controller
-    tag: "v1.0.4"
-    digest: sha256:545cff00370f28363dad31e3b59a94ba377854d3a11f18988f5f9e56841ef9ef
+    tag: "v1.2.1"
+    digest: sha256:5516d103a9c2ecc4f026efbd4b40662ce22dc1f824fb129ed121460aaa5c47f8
     pullPolicy: IfNotPresent
     # www-data -> uid 101
     runAsUser: 101