Implement value overrides mechanism for 'zgw.zaken-api.rollen.rol' resource

[MLenterman]

Implement value overrides mechanism for 'zgw.zaken-api.rollen.rol' resource, so that empty values after translating ZDS role to ZGW role can be optionally overridden when configured in the "valueOverrides" section of the translation profile.

• Apply value overrides mechanism after the translation from ZDS role to ZGW role (Just like zgw.zaken-api.zaken.zaak).
• Refactor role related XSD's to only validate elements that should be translated to JSON as an array. This way we don't have to concern ourselfs with the order of elements, which JSON doesn't care about either.