Add support for datastore configuration OSGi DS injection

Controller's blueprint component has "clustered-app-config" stanza, which allows injection of root component from the configuration datastore into projects.

This also supports inline value definition via CDATA, which is interpreted as an XML fragment, or an explicit XML file to be loaded up if the data does not exist in the datastore. See org.opendaylight.controller.blueprint.ext.DataStoreAppConfigMetadata for the gory details.

Since we are moving away from Blueprint, we need a replacement component, one which will hopefully play nicely with OSGi DS.