Display Individual Progress Indicators for Concurrent File Uploads

[xuang7]

Purpose:

Fixes issue #3421 when uploading multiple files at once, only the first upload’s progress box was shown; as soon as it finished, all remaining uploads disappeared. This PR refactors the dataset-detail upload UI so that each file gets its own independent status/progress box.

Changes:

In dataset-detail.component.ts:

• Push an initializing placeholder into uploadTasks for every file before starting its multipart upload.
• In the multipartUpload subscription, locate and update only the matching task via
  const taskIndex = this.uploadTasks.findIndex(t => t.filePath === filePath);
• Update progress, handle errors, and complete each upload per task.
• trackByTask now returns task.filePath, ensuring Angular renders a separate
  for each upload.
• Continue to auto-hide a finished task after 3 seconds, without affecting others.

In dataset-detail.component.html:

• Update file so multiple progress boxes render correctly.

In dataset-detail.component.scss:

• Wrapped the progress list in a container limited to 25vh with overflow-y: auto to keep it scrollable.

Demonstration:

Upload single file:

1file.mov

Upload multiple files:

3 files:

3files.mov

12 files:

12files.mov

[bobbai00]

Thanks for the PR! Left some comments.

[bobbai00]

LGTM!