Add migration to add disclosure_log field
user
```ruby
class AddDisclosureLog < ActiveRecord::Migration
    def self.up
        add_column :public_bodies, :disclosure_log, :text, :null => false, :default => ""
        add_column :public_body_versions, :disclosure_log, :text, :null => false, :default => ""
        add_column :public_body_translations, :disclosure_log, :text
    end

    def self.down
        remove_column :public_bodies, :disclosure_log
        remove_column :public_body_versions, :disclosure_log
        remove_column :public_body_translations, :disclosure_log
    end
end
```
assistant