Add support for sameAs

When --instance INSTANCE_NAME is provided, and that abbreviation is not matching the name prefix within identifier within what we load from dandiset.yaml record (e.g. `identifier: DANDI:000003`), we then go through sameAs entries, parse instances there and see if that INSTANCE_NAME is present -- and take the id associated with it. E.g. if `--instance EMBER-DANDI` and we have `sameAs: ['dandi://ember-dandi/000001']` -- we upload to the 000001 of the EMBER-DANDI instance.