Add registrant api companies endpoint

lib/serializers/registrant_api/company.rb

@@ -0,0 +1,20 @@
+module Serializers
+  module RegistrantApi
+    class Company
+      attr_reader :company, :country_code
+
+      def initialize(company:, country_code:)
+        @company = company
+        @country_code = country_code
+      end
+
+      def to_json(*_args)
+        {
+          name: company.company_name,
+          registry_no: company.registration_number,
+          country_code: @country_code,
+        }
+      end
+    end
+  end
+end