Prior art detection service

This is a meta-task to track activities related to providing a "prior art detection" service that can be built by composing the provenance index and the swh-scanner. One new and original use case we target is scientific publishing: when an author associates a software project with a publication, the publisher, and the reviewers, should be able to check what part of the source code is just a copy of something existing in the Software Heritage archive, and where this copied content comes from. This is different from the usual software licence compliance use case, but the underlying plumbing is similar.

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Migrated from T3136 (view on Phabricator)