Configure apache2 default modules

Hi,

In the apache2 default recipe, you directly include a list of apache2 modules to configure.
It would be great to customize this list by using the same technique as the official apache2 cookbook :

```ruby
node['apache']['default_modules'].each do |mod|
  module_recipe_name = mod =~ /^mod_/ ? mod : "mod_#{mod}"
  include_recipe "apache2::#{module_recipe_name}"
end
```

Thanks