stable/goldpinter: Only use pullSecrets if defined in values.yaml (#21823)

This was causing the DaemonSet to have an invalid key/value for imagePullSecrets

```
imagePullSecrets:
  - name:
```

Signed-off-by: Brian Glogower <xbglowx@gmail.com>

stable/goldpinger/Chart.yaml

@@ -1,6 +1,6 @@
 apiVersion: v1
 name: goldpinger
-version: 2.0.1
+version: 2.0.2
 appVersion: 2.0.0
 description: Goldpinger makes calls between its instances for visibility and alerting.
 home: https://github.com/bloomberg/goldpinger

stable/goldpinger/templates/daemonset.yaml

@@ -24,8 +24,12 @@ spec:
     spec:
       priorityClassName: {{ .Values.priorityClassName }}
       serviceAccountName: {{ template "goldpinger.serviceAccountName" . }}
+      {{- if .Values.image.pullSecrets }}
       imagePullSecrets:
-        - name: {{ .Values.image.pullSecrets }}
+        {{- range .Values.image.pullSecrets }}
+        - name: {{ . }}
+        {{- end }}
+      {{- end }}
       containers:
       - name: goldpinger-daemon
         image: "{{ .Values.image.repository }}:{{ .Values.image.tag }}"