Generate XML grammar from LutaML-UML models

[ronaldtse]

As described here: https://github.com/ietf-ribose/relaton-data-rfcsubseries/issues/4#issuecomment-1008335776 , we wish to generate XML Schema from LutaML-UML.

The XML grammar for Relaton is at:

• https://github.com/relaton/relaton-models/tree/main/grammars

The LutaML models for Relaton are at:

• https://github.com/relaton/relaton-models/tree/main/models

The LutaML-UML task is at: lutaml/lutaml-uml#96