archiving/nsg: include HDF5 exports

[sanjayankur31]

The archival does not currently include HDF5 files. This function needs to be updated:

https://github.com/NeuroML/pyNeuroML/blob/development/pyneuroml/archive/__init__.py#L107

[YBCS]

@sanjayankur31 can I work on this ?

[sanjayankur31]

This one already has a partial PR, so maybe work on #279 first and if this is still open when you're done there, we can look at this one.