Initial version of ComponentGetter. A wrapper to ease the transition to GaudiConfig2

The ComponentGetter here is meant to ease the transitions to GaudiConfig2. The version here is a simple wrapper around the existing CfgMgr. Next step is to update all ComponentAccumulator-based configuration files to use the ComponentGetter instead of the from Package.PackageConf import Component syntax. Once we are ready to switch over to GaudiConfig2-based configurables. The implementation here can be replaces by the implementation show in !28766 (closed) without changing any client code.