Append content to a file using MachineConfig is not working in Openshift 4

Issue

• How can I append content to a file using machine-config-operator?

• Trying to append content to a file inside RHCOS using MachineConfig, MachineConfigPool throws the error:

  $ oc get mcp worker -o jsonpath='{.status.conditions[?(@.type=="RenderDegraded")].message}'
  Failed to render configuration for pool worker: parsing Ignition config spec v3.1 failed with error: config is not valid
  Report: error at line 1 col 67: json: cannot unmarshal bool into Go struct field File.storage.files.append of type []types.Resource