Add search for external users

app/models/consumer.rb

@@ -2,6 +2,7 @@ class Consumer < ApplicationRecord
   has_many :users
 
   scope :with_internal_users, -> { where('id IN (SELECT DISTINCT consumer_id FROM internal_users)') }
+  scope :with_external_users, -> { where('id IN (SELECT DISTINCT consumer_id FROM external_users)') }
   scope :with_study_groups, -> { where('id IN (SELECT DISTINCT consumer_id FROM study_groups)') }
 
   validates :name, presence: true

app/models/user.rb

@@ -1,7 +1,7 @@
 class User < ApplicationRecord
   self.abstract_class = true
 
-  ROLES = %w(admin teacher)
+  ROLES = %w(admin teacher learner)
 
   belongs_to :consumer
   has_many :study_group_memberships, as: :user