Documents helper for image pull secrets

Addressing a question @grantmiller asked about whether we recommend using a Helper or not for image pull secrets.

Author: crdant

docs/vendor/helm-image-registry.mdx

@@ -46,8 +46,52 @@ To configure your application to use the proxy registry with Helm CLI installati
      .dockerconfigjson: {{ .Values.global.replicated.dockerconfigjson }}
    {{ end }}
    ```
-   
-1. Add the image pull secret that you created to any manifests that reference the image.
+1. Add a Helm helper for the image pull secret to your `_helper.tpl`. This code will use your secret but allow your customer to override it for situations, like an airgapped installation, where they have moved the image to another regitsry:
+
+```yam1
+{{/*
+Image pull secrets
+*/}}
+{{- define "replicated.imagePullSecrets" -}}
+  {{- $pullSecrets := list }}
+
+  {{- with ((.Values.global).imagePullSecrets) -}}
+    {{- range . -}}
+      {{- if kindIs "map" . -}}
+        {{- $pullSecrets = append $pullSecrets .name -}}
+      {{- else -}}
+        {{- $pullSecrets = append $pullSecrets . -}}
+      {{- end }}
+    {{- end -}}
+  {{- end -}}
+
+  {{/* use image pull secrets provided as values */}}
+  {{- with .Values.images -}}
+    {{- range .pullSecrets -}}
+      {{- if kindIs "map" . -}}
+        {{- $pullSecrets = append $pullSecrets .name -}}
+      {{- else -}}
+        {{- $pullSecrets = append $pullSecrets . -}}
+      {{- end -}}
+    {{- end -}}
+  {{- end -}}
+
+  {{/* use secret created with injected docker config */}}
+  {{- if hasKey ((.Values.global).replicated) "dockerconfigjson" }}
+    {{- $pullSecrets = append $pullSecrets "replicated-pull-secret" -}}
+  {{- end -}}
+
+
+  {{- if (not (empty $pullSecrets)) -}}
+imagePullSecrets:
+    {{- range $pullSecrets | uniq }}
+  - name: {{ . }}
+    {{- end }}
+  {{- end }}
+{{- end -}}
+```
+
+1. Use your helper in any manifests that reference the image.
 
    **Example:**
 
@@ -59,11 +103,8 @@ To configure your application to use the proxy registry with Helm CLI installati
         - name: api 
       # Access the registry, repository, and tag fields from the values file
             image: {{ .Values.images.api.registry }}/{{ .Values.images.api.repository }}:{{ .Values.images.api.tag }}
-            # Add the pull secret
-            {{ if .Values.global.replicated.dockerconfigjson }}
-            imagePullSecrets:
-              - name: replicated-pull-secret
-            {{ end }}
+            # Add the pull secret with your helper
+            {{- include "replicated.imagePullSecrets" . | nindent 6 }}
     ```
 
 1. Package your Helm chart and add it to a release. Promote the release to a development channel. See [Managing Releases with Vendor Portal](releases-creating-releases).