Add prefork configuration to benefit from multiple workers servicing requests

[ovlords]

It has been observed (from certain real world AEM installations) that enabling the prefork module improves the efficiency of the Dispatchers in serving cached content. See: https://httpd.apache.org/docs/2.4/mod/prefork.html

To enable it, add the following content in "dispatcher-conf-templates/prefork.conf.epp".
This will provide a template for all future customizers of AEM to take notice of this module.

<IfModule mpm_prefork_module>
  StartServers        8
  MinSpareServers     5
  MaxSpareServers     20
  ServerLimit         256
  MaxRequestWorkers      256
  MaxRequestsPerChild    4000
  ListenBacklog       511
</IfModule>

Test this feature to ensure we are getting the benefits of the prefork module.