save code now moderation UI

A Web-based moderation UI is needed for the save code now functionality.

It should allow to review the pending save origin requests that are yet to be approved. A restricted set of moderators (initially Software Heritage staffers, but the possibility of adding accounts for externals) should be able to approve/deny pending requests.

Additionally, it should be possible to whitelist and blacklist URL patterns based on the incoming requests.

Migrated from T1120 (view on Phabricator)

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