Allow users to upload multiple submission files in a single request

Is your feature request related to a problem? Please describe.
When a submission has multiple supporting files or figures, it can be very time consuming for the user to upload them one by one

Describe the solution you'd like
Allow users to upload multiple files in the workflow stages and document manager.
Similarly, they should be able to select and delete multiple files at once

Additional context
Since they won't be able to set a label for each file, users must be able to edit file labels after uploading multiple files. Perhaps we can enumerate them once they are uploaded (If the provided label is 'figure', set the labels to 'figure 1', 'figure 2' etc.

Start by locating the workflow-stage upload controls and the document manager, then trace how file selection, deletion, labels, and requests are handled. Define how multi-file upload, bulk deletion, and post-upload label editing should work together, including the proposed numbered labels. Done means users can perform these operations consistently in both locations with appropriate coverage.