Threaded downloads

[aguest-kc]

Description:

Use threading for the S3 renaming and downloading steps in the Spark download process.

Technical Details:

Requirements for PR Merge:

1. Unit & integration tests updated
2. API documentation updated (examples listed below)
   1. API Contracts
   2. API UI
   3. Comments
3. Data validation completed (examples listed below)
   1. Does this work well with the current frontend? Or is the frontend aware of a needed change?
   2. Is performance impacted in the changes (e.g., API, pipeline, downloads, etc.)?
   3. Is the expected data returned with the expected format?
4. Appropriate Operations ticket(s) created
5. Jira Ticket(s)
   1. DEV-0

Explain N/A in above checklist: