[COOK-3804] Use the correct datatype for apache/default_modules in `metadata.rb`

Signed-off-by: Seth Vargo <sethvargo@gmail.com>
[COOK-3800] Add `identifier` parameter to `apache2_module` definition

Some modules don't have normal identifiers of name_module and so the LoadModule directive won't work. This provides a parameter to change that identifier if you don't want the default.

Signed-off-by: Seth Vargo <sethvargo@gmail.com>
[COOK-2572] Add mod_pagespeed recipe to apache2

Signed-off-by: Seth Vargo <sethvargo@gmail.com>