complete object storage mirror on AWS

Similarly to T691, we would like to have a complete object storage on AWS, to allow researchers to perform large-scale analysis on the archive. We //almost// have it, thanks to an initial copy done by @seirl a while ago, we would like to complete it (either by periodic exports, or by keeping it in sync with the main object storage).

cc: @rdicosmo (who pointed out this need)

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Migrated from T1899 (view on Phabricator)