MuonR4 - Introduce barebone digitization tool serving as template for all sub detector digitizations

• Introduce the MuonR4::MuonDigitizationTool. The tool serves as a pure barebone for all muon digitization tools. It implements the storeGate / pile-up service access for all muon detector technologies. To implement thedigitization for a detector technology, the tool needs to inhert from this tool and overwrite

            StatusCode initialize() override; 
            virtual StatusCode digitize(const EventContext& ctx,
                                        const TimedHits& hitsToDigit,
                                        xAOD::MuonSimHitContainer* sdoContainer) const = 0;

Extra helper methods are provided to fetch containers from StoreGate/Conditions & to dump the final digits to the output container.

Tagging: @emoyse, @tlari, @mbandier, @junpei, @pscholer

Targets: ATLASSIM-5203 / ATLASSIM-6655