Secure Download of Large file exports

[YazeedLoonat]

This is tied to: #4371
and breaks the recommendation down into its 3 component pieces:

1. Setup a private S3 bucket under the exygy account For Core and HBA. Issue: Setup a private S3 bucket under the exygy account For Core and HBA #4590

2. Change the way send the export to the requesting user. Issue:
   Change the way send the export to the requesting user #4591

3. Set up doorway's either new S3 Bucket or update the current S3 bucket to have a private tag or portion that is not accessible to the general public without the URL. issue: Set up doorway's either new S3 Bucket or update the current S3 bucket #4592

[ludtkemorgan]

We will need design input on how to handle the change from the frontend, be it either an email or the new link on the UI

[sarahlazarich]

break out a separate UI ticket for when we have design feedback, prework can be done in advance
4590 includes connecting to AWS? Bc we don't have that - YL included links to review on that