investigate and document google drive export

This is an issue that will require some digging in undocumented code.

**Issue:** we have a google drive export file in im-tables - see https://github.com/intermine/im-tables/blob/dev/src/utils/send-to-google-drive.js

google drive export is something we've never really used and I'm not sure if it's feature-complete. If it _isn't_, we should either complete it or remove it. If it _does_ work when enabled, we should document how to enable it and how to use it!

Start by reading src/utils/send-to-google-drive.js and tracing how the export is enabled and used in im-tables. Determine whether the existing Google Drive export works; done means either completing or removing the incomplete feature, or documenting its enablement and usage if it works.

Written by the indexing model from the issue text.