Superblockify: Export GeoJSON, not GeoPackage

[MoritzStefaner]

Superblockify is the only algorithm shipping .gpkg, so our import shells out to ogr2ogr. That makes GDAL
a hard prerequisite for anyone running the pipeline, in an otherwise pure-Node project.

Ask: one GeoJSON per layer

for layer, gdf in {"edges": edges, "blocks": ltns, "boundary": boundary}.items():
    gdf.to_crs(4326).to_file(
        f"{slug}-superblockify-{layer}.geojson", driver="GeoJSON", RFC7946="YES"
    )

[mszell]

Either a potential job for @cbueth (see BikeNetKit/superblockify#132) or we write a conversion script.