The latest deposit v0.12 introduced that key to improve upon the metadata-only deposit.
It writes a new metadata information in the raw extrinsic metadata and declares the
deposit uri of the server as the authority (the value of swh_authority_url).
Without this, the metadata-only deposit will fail on a KeyError. Effectively failing the
docker-dev tests.
Related to T3144#60940
Related to D5258