SiteHeader: Test if multiple accounts are visible correctly and switching accounts works

[maany]

Description

If multiple logins are present, then the site header must show them.
We need to write a test to ensure this functionality works.

Also, we must test that logging out of a single endpoint sends the correct request to the logout endpoint

Motivation

No response

Change

No response

Additional Information

• The Rucio API needs to be changed.