Pass collection + id to the checker instead of an URL.

This allows the checker to use a configurable URL, in case it needs an URL different from the one used by the client.

For example a client outside docker would use http://localhost:5080/deposit/ to access the API, but the checker cannot use this URL (it needs either nginx or swh-deposit as hostname).

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Migrated from D3124 (view on Phabricator)