Add support for importing the tsv that meetup exports into a list of
upserted attendees, and event-attendee joins.
Change-Id: I5f4ddc9fc63bcc6b0334bc3e1d3cbc4d5b99c21b
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4570
Tested-by: BuildkiteCI
Reviewed-by: grfn <grfn@gws.fyi>
Autosubmit: grfn <grfn@gws.fyi>
