Refactor mtj decorations

Yannis Maznasrequested to merge
imaznas/athena:refactor-mtj-decorations into main

This is an extension of !67323 (merged) i.e. a refactor to handle decorations in MultiTrajectory and in for-now-named TrackStorageContainer classes with Aux containers. Code developed mostly by @tbold

related to EFTRACK-325

Edited by Yannis Maznas

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