Forcing (often?) requires padding

[BSchilperoort]

When generating forcing, the forcing might not work correctly if there is no padding around the clonemap. This is easily fixable by adding padding, but it would be better if this padding was added automatically in the recipe.

Current workaround:

clonemap_extents = {
    "Rhine": {"latitude": (45.0, 54.0), "longitude": (3.0, 13.5)},
}

# Set the extent of the forcing data suffiently larger than the clonemap.
esmvaltool_padding = 1.5  # degrees lat/lon
x0, x1 = clonemap_extents[catchment]["longitude"]
y0, y1 = clonemap_extents[catchment]["latitude"]

forcing = ewatercycle.forcing.sources["PCRGlobWBForcing"].generate(
    dataset="ERA5",
    start_time="2001-01-01T00:00:00Z",
    end_time="2005-12-31T00:00:00Z",
    shape="Rhine.shp",
    start_time_climatology="2001-01-01T00:00:00Z",
    end_time_climatology="2005-12-31T00:00:00Z",
    extract_region={
        "start_latitude": y0 - esmvaltool_padding,
        "end_latitude": y1 + esmvaltool_padding,
        "start_longitude": x0 - esmvaltool_padding,
        "end_longitude": x1 + esmvaltool_padding,
        },
    )