Fixes 500 errors when viewing an Organization in the Django Admin

[jkachel]

What are the relevant tickets?

n/a

Description (What does it do?)

Noticed that the Django Admin consistently returns a 500 when viewing a B2B organization in the Django Admin in production. This hopefully fixes that by prefetching the user and specifically displaying only the user email for the UserOrganizationAdminInline.

This also removes the add/change/delete permission from the inline. If you want to manage admins, you can do that from the individual user's edit screen in the Django Admin.

How can this be tested?

View an organization page in the Django Admin. It should work as expected. Ideally, use an org that has some managers set up in it. You can set that up in the user record.

Additional Context

Assuming this will help - the page takes a while to load and then errors out with a 502, but the Django process doesn't ever fail really so there's no Sentry error pointing to something specific. I can't reproduce this on RC or locally. But, the User model can be pretty unwieldy to load so this seemed like a good place to start.

[github-actions]

OpenAPI Changes

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[rhysyngsun]

I think this is a better served with @admin.display (see the third example here), since this is very specific to django-admin.

[jkachel]

Fixed in 3ac1482

[rhysyngsun]

LGTM