support software deposit via SWORD protocol (meta task)

The SWORD protocol (homepage) is used by several digital repository to exchange/replicate deposited data. We would like to enable Software Heritage to be a SWORD server capable of receiving deposits from SWORD clients. A first potential use case for this is receiving deposits of source code from HAL, but other use cases are upcoming too.

This meta-task will track the work needed to SWORD-Enable Software Heritage.

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Migrated from T647 (view on Phabricator)