Draft: Add .dtd file back in to Athena

Taking over from !48056 (closed)

Try to solve .dtd issues in ATLSWUPGR-146 which are currently causing all Run4 simulation to fail.

Longer-term we may be able to solve this a more elegant way, but in the meantime we should resolve this problem so that we can see if there is other fallout from the move to an external GeoModelXml

FYI @dellacqu @boudreau @tsulaia @mbandier @rbianchi @jchapman