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.
