📦 Download and refresh ATL11 Zarr data up to 20210421

Updating the ATLAS catalog to include ATL11 data up to and including 20210421, about five months of extra data over 2c755d5. Had to temporarily downgrade (locally, again) to fsspec=0.7.4 and intake-xarray=0.3.2 for the ATL11 intake download code in atl06_to_atl11.ipynb to work. Yes, taking a shortcut this time by pulling the official ATL11.003 data straight from NSIDC instead of wasting a week processing it ourselves. Glad that they have cycle 03 to cycle 09 in a single HDF5 file!!

Doing more preprocessing in the atl06_to_atl11.ipynb script by adding a set_xy_and_mask function which does lon/lat to x/y coordinate conversion and masking out of low quality data points. Should save some hassle in atl11_play.ipynb. Using 2 cores instead of 8 because of memory restrictions on the HPC cluster. So yeah, basically a quick refresh over d9ad9db.