Following the suggestion from @dmbaturin on https://github.com/vyos/vyos-1x/pull/481 the XML definition used by the router CLI code should be included on the router.
Upon discussion, it was agreed that the files should be added onto /usr/share/vyos.
While currently, the name of the data folders in the repo are interface-definitions and op-mode-defintion, it is felt that the aggregated XML files should be placed under
/usr/share/vyos/xml/configuration.xml and /usr/share/vyos/xml/operational.xml.
(I would assume that name interface came from early development when only interfaces definition were included, with time the XML came to have more and more configuration mode command and it feel right to correct this naming).