Allow elements from other namespaces

[malarzm]

This is how we should ideally allow extensions to be combined with ODM's schema. Sadly, this does not work and it seems work on extensions' maintainers is needed anyway :(

Cross referencing https://github.com/doctrine-extensions/DoctrineExtensions/issues/2318

[greg0ire]

Sadly, this does not work and it seems work on extensions' maintainers is needed anyway

I think it's because the extension xsd file is not provided here: https://github.com/doctrine/mongodb-odm/blob/c9b7f6bdec37f32c2b91637adeee52949e7596e6/lib/Doctrine/ODM/MongoDB/Mapping/Driver/XmlDriver.php#L718-L720

You'd have to let the user provide a schema combining both xsd files as in https://github.com/doctrine/orm/issues/11117#issuecomment-1894492234

[malarzm]

@greg0ire thanks for all the pointers! I'll prolly join you in https://github.com/doctrine/orm/issues/11123 soon