Use the `target` argument to RawExtrinsicMetadata instead of deprecated `id`
This argument was deprecated in swh.model v0.7.2
Test Plan
python3 -m pytest -sv --ff -W error:RawExtrinsicMetadata:DeprecationWarning -n 6 (no deprecation warnings left, when using swh.storage master)
Migrated from D4402 (view on Phabricator)