Concurrent file uploads result in incorrect dataset_id reservations

[renato2099]

Ingesting multiple files concurrently (e.g., coming from zip files) can easily lead to submission's not being associated with the same dataset's. This can happen if no transaction has reserved a dataset_id yet therefore a file from the same dataset reserves a new dataset_id at the same time.

We can remedy this in the following ways...

1) Temporary workaround: disable parallel uploads from:

result = parmap.map_async(
        process_etuff_file,
        etuff_files,
        version=version,
        notes=notes,
        pm_parallel=False,         <<<<<<<<<< N.B. Sequential ingestion
        pm_processes=cpu_count(),
    )

2) Split metadata ingestion from content ingestion, that would reduce the possible window of concurrent transactions. Additional brainstorming and ingestion logic is required in order to perform multi-file paralle ingestion.

This issue came to light when we began to accomodate multi-track submissions in parallel.

[lewismc]

Addressed in #286