Create a configuration file per cluster group

Currently, the etc/org.apache.karaf.cellar.groups.cfg gathers configuration for all groups (features, bundles, blacklist, whitelist, ...).
When you use a large number of cluster groups, this file is not easy to read and maintain.
I will create a configuration file dedicated per cluster group, like for instance etc/org.apache.karaf.cellar.groups.default.cfg and etc/org.apache.karaf.cellar.groups.mygroup.cfg.