Configuration option for security.limit_extensions and listen.owner/listen.group/listen.mode properties

I needed to configure the security.limit_extensions property in the pool configuration file. My changes preserve the default behaviour (allowing only ".php" files) unless configured otherwise.
Tested and works locally.

UPDATE: 1: 've also added changes to be able to configure the owner/group for the unix socket. Same applies here: Not adding configuration will keep default behaviour.

UPDATE 2: I've now also added a configuration option for listen.mode to my changes. Keeping default if not set on the node.