LPS-46754 Custom DL converters for staging

Hey Brian,

We have recently sent you the adapter for the XStream converters and this pull request contains the actual custom converters for DL.

In some cases (eg. Documentum hook) the file entries are being handled with a proxy object. This caused serialization issues during an export and import (the classloader was serialized, or a documentum specific class, etc). @akosthurzo implemented the solution which was to create custom converters for specific entities. The XStream takes these registered converters and uses them to serialize certain objects (depending on the canConvert method's return value).

While this has been introduced to fix a bug for DL export/import we took to opportunity and provide a framework for developers in case they want to leverage this later on, and Ákos built his solution on the top of this in collaboration with me.

Thanks,

Máté

cc: @sergiogonzalez