Provide tools & setup for tracking of Heavy Ion on ITk events in standalone ACTS environment

The goal is to work out tools & setup to demonstrates ACTS tracking chain on for Heavy Ion events in ATLAS ITk detector.
In comparison to an existing chain the HI reconstruction is likely to need fast vertex z estimation and a modification to the seeding that would allow to contain the seeds to that vertex only. (Default chain should be obviously tried first to obtain reference.)
The project is covered by Petr Bolek.

A concrete work items are:
- review existing vertex Z finders
- implement the vertex Z finder in ACTS
- consider implementations suitable for accelerators (not the 1st priority)
- implement example algorithm using it
- extend the functionality of the seed finder to also accept z vertex constraint (not only beam spot position & mag field as is now)
- optimise setup
- consider adding plugin to hijing generator - only if particle gun will be deemed insufficient for testing - coordinate with @plariono who works on ALICE on it
- integrate the solution with Athena