Add grouped properties for SWHID target in ERMDS API endpoint

The origin property is misleading in the ERMDS endpoint, because it seems it is the origin of the metadata (which is false, this is the origin of the content that is described, taken from a full SWHID). We wish to group all SWHID info under a higher level property target-details or target-info or other.

Here is the result at the moment:

[
    {
        "authority": {
            "type": "deposit_client",
            "url": "https://inria.halpreprod.archives-ouvertes.fr/"
        },
        "discovery_date": "2021-10-20T14:22:49+00:00",
        "fetcher": {
            "name": "swh-deposit",
            "version": "0.14.3"
        },
        "format": "sword-v2-atom-codemeta",
        "metadata_url": "https://webapp.staging.swh.network/api/1/raw-extrinsic-metadata/get/303a4b7518c573acde54cdb0b35603a340e33316/?filename=swh:1:dir:bc14367a8c9b7f70c49fa6a75244cef19db28ada_metadata",
        "origin": "https://github.com/moranegg/AffectationRO",
        "revision": "swh:1:rev:e3b5164418d287dc8760c40a00751dc19673b3e1",
        "snapshot": "swh:1:snp:3d73c454047658280dbbf7a5fbc3c25f788d4a37",
        "target": "swh:1:dir:bc14367a8c9b7f70c49fa6a75244cef19db28ada"
    }
]

We wish to have:

[
    {
        "authority": {
            "type": "deposit_client",
            "url": "https://inria.halpreprod.archives-ouvertes.fr/"
        },
        "discovery_date": "2021-10-20T14:22:49+00:00",
        "fetcher": {
            "name": "swh-deposit",
            "version": "0.14.3"
        },
        "format": "sword-v2-atom-codemeta",
        "metadata_url": "https://webapp.staging.swh.network/api/1/raw-extrinsic-metadata/get/303a4b7518c573acde54cdb0b35603a340e33316/?filename=swh:1:dir:bc14367a8c9b7f70c49fa6a75244cef19db28ada_metadata",
        "target-details":  {
             "origin": "https://github.com/moranegg/AffectationRO",
             "revision": "swh:1:rev:e3b5164418d287dc8760c40a00751dc19673b3e1",
             "snapshot": "swh:1:snp:3d73c454047658280dbbf7a5fbc3c25f788d4a37",
             "target": "swh:1:dir:bc14367a8c9b7f70c49fa6a75244cef19db28ada"
       }
    }
]

Example taken from: https://webapp.staging.swh.network/api/1/raw-extrinsic-metadata/swhid/swh:1:dir:bc14367a8c9b7f70c49fa6a75244cef19db28ada/?authority=deposit_client%20https://inria.halpreprod.archives-ouvertes.fr/

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Migrated from T3676 (view on Phabricator)