Add node labels to ugrid netcdf

[evetion]

Now that we simplify our network for Delwaq coupling, debugging something like the HWS model becomes a pain. It would help to store the node labels (Eijsden grens) in our ugrid output as well.

[visr]

If I remember correctly, if you add a string variable it won't open anymore in QGIS since MDAL doesn't support it.

[Huite]

A pragmatic solution for now: if you have the xugrid representation of the network, you can convert it with some associated data directly to a geodataframe in a single to_geodataframe() call. Then write to a geopackage I guess, and at least you'll be able to see the IDs in QGIS:

https://deltares.github.io/xugrid/api/xugrid.UgridDataArrayAccessor.to_geodataframe.html