Modernise CscOverlay overlayContainer method

This is a first part of the CscOverlay cleanup and modernisation

• Rewrite overlayContainer as it was done for other muon overlay algorithms (see !21148 (merged) and !21454 (merged)).
• Make a new universal copyCollection function.
• Try to do as little type conversions as possible.
• Try to move to the new recommended overlay naming for the changed functions.
• Not sure if needed, but move MAX_AMPL to the anonymous namespace.

mergeCollections method will be fully cleaned up in a follow-up MR. Also all output-changing stuff will be changed later.

This MR should not change the output.