Add a log file to track deleted duplicate records

It might be interesting in some cases to check the information related
to those records.

app/lib/duplicate_records_logger.rb

@@ -0,0 +1,21 @@
+class DuplicateRecordsLogger
+  def info(message)
+    logger.info(message)
+  end
+
+  def logger
+    @logger ||= ActiveSupport::Logger.new(log_file).tap do |logger|
+      logger.formatter = Rails.application.config.log_formatter
+    end
+  end
+
+  private
+
+    def log_file
+      File.join(File.dirname(Rails.application.config.default_log_file), log_filename)
+    end
+
+    def log_filename
+      "duplicate_records.log"
+    end
+end