Add option to manage secrets outside of helm

So that a user can manage the nodepool config file (which is a secret)
outside of helm, add an option where the user can specify the name
of that secret as a value, and if it's set, helm will not write the
secret and will tell k8s to mount that secret as the nodepool config
instead.

Change-Id: Ifa1b5e81b6c7700faef82f3b18aab157d042e735

charts/nodepool/templates/builder/statefulset.yaml

@@ -40,7 +40,7 @@ spec:
       volumes:
       - name: nodepool-config
         secret:
-          secretName: {{ include "nodepool.fullname" . }}
+          secretName: {{ (empty .Values.config.secret) | ternary (include "nodepool.fullname" .) .Values.config.secret  }}
       - name: nodepool-logs
         emptyDir: {}
       - name: dev

charts/nodepool/templates/launcher/deployment.yaml

@@ -31,7 +31,7 @@ spec:
       volumes:
       - name: nodepool-config
         secret:
-          secretName: {{ include "nodepool.fullname" . }}
+          secretName: {{ (empty .Values.config.secret) | ternary (include "nodepool.fullname" .) .Values.config.secret  }}
     {{- with .Values.tolerations }}
       tolerations:
 {{ toYaml . | indent 8 }}

charts/nodepool/templates/secret.yaml

@@ -1,4 +1,5 @@
 ---
+{{ if not .Values.config.secret }}
 apiVersion: v1
 kind: Secret
 metadata:
@@ -11,4 +12,5 @@ stringData:
 {{ toYaml .Values.config | indent 4 }}
   clouds.yaml: |
     clouds:
-{{ toYaml .Values.clouds | indent 6 }}
+{{ toYaml .Values.clouds | indent 6 }}
+{{ end }}