Clustering : Add reference.conf in sal-akka-raft and clustering-commons

Per akka guidelines,
1. All libraries should provide a reference.conf files with defaults.
2. All applications should provide application.conf files. In our case, akka.conf contains appilcation configuration. We need to remove application.conf from sal-remoterpc-connector and distributed-datastore. Since akka merges all configurations (reference.conf, application.conf, akka.conf), we may see unwanted configurations if we dont remove application.conf.