Recreate search + transfer pipeline using ESGF's python package (`esgpull`)

[Joshdpaul]

https://esgf.github.io/esgf-download/

Using this package may improve certain parts of the CMIP6 (and CMIP7) transfers pipeline (i.e., the data search > audit for completeness > data download). It looks like search and audit tasks could be streamlined by using this app (see facet search here - looks better than our current ls-based file system search process), but it's unclear if the download task would be better performed via Globus as we have done in the past.