Change parameter `slug` in swh-deposit cli to `create_origin`

We want to deprecate the usage of slug for the origin.

Plan:

• !207 (closed): Deprecate use of the --slug and expose --create-origin
• !213 (closed): Checks the XML client provided contains at least swh:create_originor swh:add_to_origin and shows a warning if it's missing

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Migrated from T2860 (view on Phabricator)