adds a factory for conversation participants

Author: Kneeba921

spec/factories/better_together/conversation_participants.rb

@@ -1,6 +1,10 @@
 # frozen_string_literal: true
 
 FactoryBot.define do
-  factory :conversation_participant do # rubocop:todo Lint/EmptyBlock
+  factory('better_together/conversation_participant',
+          class: 'BetterTogether::ConversationParticipant',
+          aliases: %i[better_together_conversation_participant conversation_participant]) do
+    association :conversation
+    association :person
   end
 end