ComponentAccumulator migration to GaudiConfig2
This MR is a rearranged version of hugh MR !30675 (closed). Same code changes but in a tidy commit history. It included (and superseeds) @rlangenb MR !31795 (closed).
The code-changes here contain substantial contributions from @tbold, @aporeba, @fwinkl and @khoo. These colleagues also checked the code changes, so this MR can be considered 'expert-reviewed' (at least in parts).
All CI tests are supposed to work but I am aware that some ART-test using new config still fail.