Admin/Quota page takes too long to load - requests to much information

[bgruening]

Describe the bug

Opening the Admin->Quota page or the "Create New quota" page takes a long time on EU. It seems that we transfer 6MB of data and this takes roughly 6s.
I think we request all groups and all users with those API calls. At least for the "/admin/quotas" page, that should not be necessary. I'm unsure if we need to load all users for "admin/form/create_quota".

Galaxy Version and/or server at which you observed the bug
Galaxy Version: 24.2 (but this problem exists most likely since a long time)

To Reproduce
Steps to reproduce the behavior:

1. You need to be admin
2. Go to 'https://<your_galaxy>/admin/quotas'
3. See in the browser console how long the page load takes and what is requested

Expected behavior
Page should load faster.

Additional context
Not a very important bug/issue.

[jdavcs]

Related #17709 (same problem, different admin area)