Resolve "Switch Affiliation"

Closes #377 (closed)

Only available when logged in with keycloak. We cannot add it when logged in with DB as it would require saving the password in local storage.

Would be good to add:

• Send current affiliation too in the usersByPrefix list so that we can display it too as selected (currently we know which ones we can go to but do not know which one is selected).
• Anything else that the date to help figure out what each affiliation corresponds to. (email? roles?)