Add dual-use TrackParticleMergerAlg

@dguest was annoyed that we needed to use athena to merge two track collections. Hopefully this makes him less annoyed.

This MR adds a new CP algorithm to TrackingAnalysisAlgorithms which takes two TrackParticleContainers and merges them into one to be more easily fed into downstream algorithms.

Note: The old TrackParticleMerger in the DerivationFrameworkInDet needs to be removed, but there are quite a few places where it will need to be modified to use the new alg. I will follow this up in a separate MR.

Also tagging @svanstro

Edited by Jackson Carl Burzynski

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