[DRAFT] PWGLF: Add continuously-increasing-with-Nch xi/om injection

[ddobrigk]

@njacazio draft only, for your consideration / for discussion - seems to work but some of it is written in very unpolished ways.

This PR leverages the (fantastic) flexibility of the current o2sim machinery to inject a certain number of Xi and Omega baryons into Pb-Pb events, with the "certain number" depending on the charged-particle multiplicity and being specifically tailored to reproduce the measured Xi/Pi and Omega/Pi ratios versus Nch. This figure from the previous ALICE 3 use case illustrates the principle:

The advantage of this injection scheme is that it provides a continuously and realistically varying number of injected particles. At base configuration, the actual number will in fact match 1:1 the expected real yield. Having that in mind, in fact: for the sake of computing efficiency, we could also consider adding a floating-point modifier to scale the Xi/Pi and Omega/Pi curves upwards or downwards.

[github-actions]

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