Use consistent quoting for file-based backup annotations

[smlx]

Checklist

• Affected Issues have been mentioned in the Closing issues section
• Documentation has been written/updated
• PR title is ready for changelog and subsystem label(s) applied

The old quoting was causing backup breakage.

Before we had:

annotations:
  k8up.syn.tools/backupcommand: /bin/sh -c "/bin/busybox tar -cf - -C {{ .Values.persistentStorage.path | quote }} ."

After templating this will have invalid quoting (" inside "):

annotations:
  k8up.syn.tools/backupcommand: /bin/sh -c "/bin/busybox tar -cf - -C "/my/path/example" ."

This PR changes the template to:

annotations:
  k8up.syn.tools/backupcommand: /bin/sh -c '/bin/busybox tar -cf - -C {{ .Values.persistentStorage.path | quote }} .'

After templating the quoting is valid for the shell command:

annotations:
  k8up.syn.tools/backupcommand: /bin/sh -c '/bin/busybox tar -cf - -C "/my/path/example" .'

Closing issues

n/a

[smlx]

@tobybellwood this one will also need to be pulled into 2.x