Provide namespace for xml-file in flux

[TobiasNx]

Even though following ticket states that this is solved,

#247

One cannot add a simple namespace to an xml file with flux or its java implementation.

This should be easily possible.

[blackwinter]

Even though following ticket states that this is solved,

It's been solved for Java, not for Flux.

[TobiasNx]

It seems that this also works in the flux: https://github.com/TobiasNx/metafacture_runner_examples/blob/b94d361280f7eec816acc5e4abae8da67b7e7ae4/examples/marc21-to-edm/MARC21-EDM.flux#L18

[blackwinter]

(i.e., namespaceFile vs. namespaces)

[TobiasNx]

you are right, adding the namespace within the flux could be more convenient