Move data migrations from rake tasks to gem

See #1298

db/data/20200225085234_convert_domain_delete_date.rb

@@ -0,0 +1,19 @@
+class ConvertDomainDeleteDate < ActiveRecord::Migration[5.1]
+  def up
+    # processed_domain_count = 0
+    #
+    # Domain.transaction do
+    #   Domain.find_each do |domain|
+    #     next unless domain.delete_date
+    #
+    #     domain.update_columns(delete_date: domain.delete_date + 1.day)
+    #     processed_domain_count += 1
+    #   end
+    # end
+    #
+    # puts "Domains processed: #{processed_domain_count}"
+  end
+
+  def down
+  end
+end