Forcings Metadata layer for hydrofabric

[jduckerOWP]

Previous versions included an *ext.gpkg that included a "forcing_dem_attributes" layer. Although the NextGen forcings workstream does not need any more weights, we still need the following variables for each catchment id to perform bias calibration and downscaling techniques:

elevation
slope
aspect

You can integrate these in any way you see fit with either the current geopackages or a supplementary geopackage. Thanks again Mike!