chore: keep a useable empty dir mount even when persistence is disabled (#2124)

## Description

This PR sets up an empty dir when persistence is disable which is
something needed for the longhorn init package:

https://github.com/defenseunicorns/zarf-init-longhorn

## Related Issue

Fixes #1995

## Type of change

- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Other (security config, docs update, etc)

## Checklist before merging

- [ ] Test, docs, adr added or updated as needed
- [x] [Contributor Guide
Steps](https://github.com/defenseunicorns/zarf/blob/main/CONTRIBUTING.md#developer-workflow)
followed

---------

Co-authored-by: Ben Mountjoy <benmountjoy@gmail.com>

Author: Racer159

examples/longhorn/values.yaml

@@ -98,7 +98,7 @@ persistence:
   removeSnapshotsDuringFilesystemTrim: ignored # "enabled" or "disabled" otherwise
 
 csi:
-  kubeletRootDir: "/var/lib/kubelet" 
+  kubeletRootDir: "/var/lib/kubelet"
   attacherReplicaCount: ~
   provisionerReplicaCount: ~
   resizerReplicaCount: ~

packages/zarf-registry/chart/templates/deployment.yaml

@@ -73,10 +73,8 @@ spec:
 {{ toYaml .  | indent 12 }}
 {{- end }}
           volumeMounts:
-{{- if .Values.persistence.enabled }}
             - name: data
               mountPath: /var/lib/registry/
-{{- end }}
             - name: config
               mountPath: "/etc/docker/registry"
       affinity:
@@ -108,4 +106,8 @@ spec:
         - name: data
           persistentVolumeClaim:
             claimName: {{ if .Values.persistence.existingClaim }}{{ .Values.persistence.existingClaim }}{{- else }}{{ template "docker-registry.fullname" . }}{{- end }}
+{{- else }}
+        - name: data
+          emptyDir:
+            sizeLimit: {{ .Values.persistence.size }}
 {{- end }}