ENH: Add RKI (German) sequences that haven't yet been submitted to GISAID

[corneliusroemer]

Germany's RKI publishes received sequences daily to Github and Zenodo.

Submissions to GISAID are done only weekly. Hence Github/Zenodo is a few days ahead.

I think it would be great to use these earlier sequences in Usher - the same way you use COG-UK sequences in the Usher tree.

The repos are here: https://github.com/robert-koch-institut/SARS-CoV-2-Sequenzdaten_aus_Deutschland https://zenodo.org/record/7029082/files/robert-koch-institut/SARS-CoV-2-Sequenzdaten_aus_Deutschland-2022-08-28.zip?download=1

Also these would be a great addition to the "open" tree, after all there are >1m sequences there and unfortunately many of them haven't yet made it to Genbank @AngieHinrichs