Account for the terrain slope when calculating land-use availability for renewable generation

Describe the feature you'd like to see

Renewable generation units may have some limitations in acceptable terrain slopes where they can be installed. It's worth to add functionality to account for the slope, when calculating land availability for different renewable sources. That can be implemented using gebco dataset which we are using currently to take into account the sea shore depth for offshore wind installations.

Possible implementation

A great example by @euronion can be found in this notebook with the configuration parameters defined here. A similar calculation can be added to build_renewable_profiles in PyPSA-Earth, like it's currently done for the shore distances, e.g.:

pypsa-earth/scripts/build_renewable_profiles.py

Lines 721 to 723 in bae5586

    
           if "max_shore_distance" in config: 
        
               buffer = config["max_shore_distance"] 
        
               excluder.add_geometry(paths.country_shapes, buffer=buffer, invert=True)

	if "max_shore_distance" in config:
	buffer = config["max_shore_distance"]
	excluder.add_geometry(paths.country_shapes, buffer=buffer, invert=True)