Chore: API Improvements (#2956)

- API to fetch info of a single inbox
- Document passing custom_attributes in the API
- Ability to filter contacts with contact identifier in search API

spec/factories/contacts.rb

@@ -3,9 +3,15 @@
 FactoryBot.define do
   factory :contact do
     sequence(:name) { |n| "Contact #{n}" }
-    sequence(:email) { |n| "contact-#{n}@example.com" }
-    phone_number { Faker::PhoneNumber.cell_phone_in_e164 }
     avatar { fixture_file_upload(Rails.root.join('spec/assets/avatar.png'), 'image/png') }
     account
+
+    trait :with_email do
+      sequence(:email) { |n| "contact-#{n}@example.com" }
+    end
+
+    trait :with_phone_number do
+      phone_number { Faker::PhoneNumber.cell_phone_in_e164 }
+    end
   end
 end