Avoid duplicate polyline names in geodataframe_to_PolyFile

[veenstrajelmer]

It seems that currently all names of the separate polyfiles are the same, the below code is a user-scoped workaround used in the DSO project:

bnd_gdf = dfmt.generate_bndpli_cutland(mk=mk_object, res='h', buffer=0.01)  
bnd_gdf['name'] = f'{model_name}_bnd' # this must be changed to allow for multiple polylines in the file
bnd_gdf['nr_bnd'] = bnd_gdf.index
bnd_gdf['name'] = bnd_gdf['name'] + '_' + bnd_gdf['nr_bnd'].astype(str)  
bnd_gdf_interp = dfmt.interpolate_bndpli(bnd_gdf, res=0.06)

Properly implement this in dfmt.geodataframe_to_PolyFile() instead of bothering the user with it.