Related T857

Related T857

Summary:
- structured origin_metadata with tool and provider
- used store_metadata function in DepositLoader to add metadata to storage
Note: modification in SWHLoader (loader-core) are in another diff

Reviewers: ardumont

Differential Revision: https://forge.softwareheritage.org/D265

Fix by overriding the parsing done prior to storage in db.  This is
simpler than to use encoder for serializing the right types in the
db (which also needs a superior version of django).

Related T806

Now, we use real basic archives for testing purpose.

Separated from the query/response flow, we now check that we can at
least read deposit's archives (implementation wise, we use django's
signal api).

If the archives' check fails, the deposit is deemed 'rejected'.  The
client can check the state endpoint to know the status.
deposit_status key).  Otherwise, the status is set to
ready-for-injection.