This fixes the following error when Jinja tries to process
`mpm_prefork.conf.jinja` or `00-mpm.conf.jinja`, when it processes the
`max_request_workers` comparison:

```
Unable to manage file: Jinja error: '>=' not supported between instances of 'str' and 'int'
[...]
<IfModule mpm_prefork_module>
  StartServers {{ mpm_param['start_servers'] | d('5') }}
  MaxRequestWorkers {{ mpm_param['max_request_workers'] | d('150') }}
{%- if mpm_param['max_request_workers'] | d('150') >= 256 %}    <======================
  ServerLimit {{ mpm_param['max_request_workers'] | d('150') }}
{%- endif %}
  MinSpareServers {{ mpm_param['min_spare_servers'] | d('5') }}
  MaxSpareServers {{ mpm_param['max_spare_servers'] | d('10') }}
  MaxConnectionsPerChild {{ mpm_param['max_connections_per_child'] | d('0') }}
```

Add filters that convert the values to an int first.