Add missing export for ItemRequest module

[tdonohue]

References

Fixes #2195

Description

Somewhere along the way the ItemRequest module is no longer being exported. This results in a blank page in the UI whenever you visit an ItemRequest page:
http://localhost:4000/request-a-copy/[token]

Instructions for Reviewers

• Create a request for copy
  • Restrict a bitstream
  • Login as a user without privileges and submit a request for copy.
• As a user who can respond to the request, login and visit http://localhost:4000/request-a-copy/[token]
  • Verify on main that you see a blank page.
  • Verify that with this PR, the request a copy page loads & you can then either approve or reject the request.

[tdonohue]

This fix was recommended by Nicolas Boulay on Slack. I was able to reproduce the issue & verify the fix.

[aroman-arvo]

tested and OK

[tdonohue]

Thanks @aroman-arvo for testing on your end! Merging this as that's two people who have verified the fix.