charts: re-render the dex charts to use checksum/config

We need Dex Pods to restart when secret content change, so use the
`checksum/config` annotation on the Dex Pods. This annotation is equal
to the digest of the secret content

This chart is re-rendered using:

```
./charts/render.py dex --namespace metalk8s-auth charts/dex.yaml \
    --service-config dex metalk8s-dex-config \
    charts/dex/ > salt/metalk8s/addons/dex/deployed/chart.sls
```

Fixes: #2569

charts/dex.yaml

@@ -40,6 +40,10 @@ extraVolumeMounts:
   - name: dex-login
     mountPath: /web/themes/scality
 
+podAnnotations:
+  # Override default checksum as we want to manage it with salt
+  checksum/config: '__slot__:salt:metalk8s_kubernetes.get_object_digest(kind="Secret", apiVersion="v1", namespace="metalk8s-auth", name="dex", object_key="data:config.yaml")'
+
 certs:
   web:
     create: false

salt/metalk8s/addons/dex/deployed/chart.sls

@@ -187,7 +187,8 @@ spec:
   template:
     metadata:
       annotations:
-        checksum/config: d58a2489f8f7fd4df3f78cad5ea6ac51e7eda9ca076c41689ce853539ff2a15b
+        checksum/config: __slot__:salt:metalk8s_kubernetes.get_object_digest(kind="Secret",
+          apiVersion="v1", namespace="metalk8s-auth", name="dex", object_key="data:config.yaml")
       labels:
         app.kubernetes.io/component: dex
         app.kubernetes.io/instance: dex