vault/api_views: Implement better streaming of cooked bundle to clients

Previously a cooked bundle was streamed to clients but it was quite inefficient as it was first fully downloaded by the webapp from the vault service and then streamed to clients.

Now the webapp will simply forward the stream of cooked bundle bytes from the vault service to the Web API client, thus removing costly caching of bundle bytes in webapp memory and initiating bundle download much faster when its size is large.

Related to #4744 (closed)

CI will fail until swh-vault!183 (closed) is merged and tagged.