Feature Request/Idea: e2e test for file upload

[ErykKul]

Overview of the Feature Request
Add real e2e test at least for this cases:
Upload a single file
Upload multiple files
Upload multiple files and cancel one.
And after each test navigate to the Dataset that the files were uploaded and check they exists in the Files Table

What kind of user is the feature intended for?
(Example users roles: API User, Curator, Depositor, Guest, Superuser, Sysadmin)

What inspired the request?

What existing behavior do you want changed?

Any brand-new behavior do you want to add to Dataverse?

Any open or closed issues related to this feature request?
#431

[ErykKul]

Tracked by #417 and implemented by PR #464