Map sizes from linked files

[genie9]

Proposed solution

The total size of files linked to specific metadata should be added to Metax metadata. This information would be probably available after integration with the file upload service (SD Connect or other).
The structer is documented in https://github.com/CSCfi/metadata-submitter/blob/develop/metadata_backend/services/metax_mapper.py#L220-L223:

"total_remote_resources_byte_size": {
                "type": "integer",
            },

DoD (Definition of Done)

Published dataset discoverable in Etsin will have information on total data size.

Testing

Integration tests.

[csc-felipe]

This information should be available from the Datacite submission.

[csc-felipe]

Now that we have files in the database and the files operator, it is possible to implement this feature #627.