fix(helm): avoid null volumes in deployment (#608)

Description of changes:

The AWS ACK Helm chart generates `"volumes": null` when no static secret `.Values.aws.credentials.secretName` or no extra volume `.Values.deployment.extraVolumes` was set. This can cause issues during the deployment, particularly with admission controllers such as policy engines. An example issue can be found here kyverno/policies#1310 by Kyverno. 

This PR solves such problems without using a workaround, like deploying an unused emptyDir.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

Author: blanchardma

templates/helm/templates/deployment.yaml.tpl

@@ -148,6 +148,7 @@ spec:
         {{ "{{- if .Values.deployment.extraEnvVars -}}" }}
           {{ "{{ toYaml .Values.deployment.extraEnvVars | nindent 8 }}" }}
         {{ "{{- end }}" }}
+        {{  "{{- if or .Values.aws.credentials.secretName .Values.deployment.extraVolumeMounts }}" }} 
         volumeMounts:
         {{ "{{- if .Values.aws.credentials.secretName }}" }}
           - name: {{ "{{ .Values.aws.credentials.secretName }}" }}
@@ -157,6 +158,7 @@ spec:
         {{ "{{- if .Values.deployment.extraVolumeMounts -}}" }}
           {{ "{{ toYaml .Values.deployment.extraVolumeMounts | nindent 10 }}" }}
         {{ "{{- end }}" }}
+        {{ "{{- end }}" }}
         securityContext:
           allowPrivilegeEscalation: false
           privileged: false
@@ -195,15 +197,17 @@ spec:
       hostPID: false
       hostNetwork: {{ "{{ .Values.deployment.hostNetwork }}" }}
       dnsPolicy: {{ "{{ .Values.deployment.dnsPolicy }}" }}
+      {{ "{{- if or .Values.aws.credentials.secretName .Values.deployment.extraVolumes }}" }}
       volumes:
       {{ "{{- if .Values.aws.credentials.secretName }}" }}
         - name: {{ "{{ .Values.aws.credentials.secretName }}" }}
           secret:
             secretName: {{ "{{ .Values.aws.credentials.secretName }}" }}
       {{ "{{- end }}" }}
-{{ "{{- if .Values.deployment.extraVolumes }}" }}
-{{ "{{ toYaml .Values.deployment.extraVolumes | indent 8}}" }}
-{{ "{{- end }}" }}
+      {{ "{{- if .Values.deployment.extraVolumes }}" }}
+        {{ "{{ toYaml .Values.deployment.extraVolumes | indent 8 }}" }}
+      {{ "{{- end }}" }}
+      {{ "{{- end }}" }}
 {{ "  {{- with .Values.deployment.strategy }}" }}
   strategy: {{ "{{- toYaml . | nindent 4 }}" }}
 {{ "  {{- end }}" }}