Add affiliation field to user model

[mihow]

Add a field to store the organization or affiliation in a user profile. This is needed to help know which users are working on which projects.

• Add field in ami/users/models.py
• make a migration
• Show affiliation field in the django admin, add a filter in the list view
• Update UI for user profiles in the public UI
• Find the affiliation of all existing users, add to a spreadsheet, then update in the Django admin

[mihow]

@mohamedelabbas1996 I am assigning this to you in case you want a smaller task to knock out after we merge the big ones!