Review the deposit of CodeMeta metadata in xml (following SWORD V2 specs)

At the moment deposited metadata are in xml format using a mix of ATOM and CodeMeta, as detailed in the docs: https://docs.softwareheritage.org/devel/swh-deposit/metadata.html

There is a discrepancy, because CodeMeta vocabulary is only defined in JSON-LD and not in an XML schema.

I have discussed with @vlorentz to improve and facilitate the situation.

We have 2 options:

1. translate the JSON-LD to an XML schema
2. have a metadata-blob or codemeta property in the ATOM xml in which a codemeta.json file can be transferred as is, raw format.

The second option is easier to handle and might also be more appropriate to our new scenario with depositing only metadata.

This task can become a high priority, because we have the IPOL journal as a new SWORD client now. They are very eager to deposit published software artifacts.
At the moment I have explained how to create the xml, but I'm not satisfied of its unecessary complexity.

Also, HAL is planning on creating a codemeta.json export during the sprint (if it takes place), which is exactly the metadata-blob we want.

Task goal: choose an option and evaluate next steps for SWH deposit

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Migrated from T2311 (view on Phabricator)