Esv2yaml: Support splitting XML input into both config and content

Trying to run esv2yaml against the hippo-connect project or the properties forge plugin demo project, I run into an esv2yaml error-and-abort situation, where the tool complains that a single XML resource contains both config and content. An example for this is when the base content.xml resource contains child or sibling nodes of /content/documents, or when the duplicated auto-export rules for best-practice categorisation of HST configuration require esv2yaml to split up a resource into config and content.