Generalize HDF5 IO support

[serraramiro1]

Feature description

Currently, we have some utilities to load NDT maps from hdf5 files.
While this approach is sufficient for now, we could refactor this code so that we can reuse some bits of the hdf5 IO whenever we need it for different map types.
One example would be supporting loading in Eigen matrices, or scalars from a specific dataset and a HDF5 file.