zendesk_create_user() breaks when email address contains capital letters

Closed 🐛 Zendesk user sync not working for existing zendesk users when drupal email has capitals Closed: duplicate as a duplicate - the approach here looks better, but the code needs to be turned into a patch.

For one thing, we probably shouldn't call call() -- is there an API function to do 'create or update'?

Aha:

            'createOrUpdate'             => 'users/create_or_update.json',
            'createOrUpdateMany'         => 'users/create_or_update_many.json',