📦 Refresh ATL11 Zarr data to 20200930

Reprocessing 4160 ATL11 files with 80 CPU cores (max number) on load balancing. No hard numbers again because my browser crashed at 16%, but it took about 7 days this time. This is a new refresh over 51fc2ba, and there's an `alphashape` dependency needed by `ATL11/write_METADATA.py`. Otherwise things are pretty straightforward with no apparent schema change. Also, the official ATL11 files are out at https://doi.org/10.5067/ATLAS/ATL11.001 so this will (fingers crossed) definitely be the last time running ATL06_to_ATL11 conversions, thought the Zarr stuff will still need to happen.