add RWS bathymetry to nlmod.read.rws

[dbrakenhoff]

• add method to get configuration
• add method to download index (geodataframe)
• add method to download bathymetry data as xr.DataArray
• add tests

[rubencalje]

Great addition! I would change the following minor points:

• I would change the default resolution to 20m (unless there is a good reason for the fine resolution)
• I would add an optional parameter config to get_bathymetry_gdf and get_bathymetry, with a value of None that is replaced by the output of get_gdr_configuration when None. IN this way, when the url changes, the user can edit the configuration without a new nlmod version.

[dbrakenhoff]

The larger resolution does not return data for the major rivers, only the sea, IJsselmeer (I think) and estuaries. So I'm fine with either as the default, but there is a difference in the area both resolutions cover.

And good idea for the config, I'll add that.

[dbrakenhoff]

test fails unrelated.