SILKIT-1477 SystemController Utility: Use SignalHandler, better report state

[AndreasRentschler]

Subject

Improvements of SystemController utility

Description

SILKIT-1477 System controller blocks new participants after required participants have terminated

• SystemController did not consistently report about the system's shutdown/error state.
• Reconnecting a participant after the system went into Shutdown state made the SystemController appear to hang.
• Changed to SignalHandler approach to allow for implicit exit after shutdown (std::cin.ignore() cannot be canceled). SIgnalHandler had to be turned into a reusable module, previously owned by Registry utility.
• Bugfix: Warning on valid transition from Aborting to Shutdown
• RequestReply was ignored when barrier has not yet been passed. Now, a warning is emitted and the new RequestReply is executed.

Instructions for review / testing

• SignalHandler, refactored for public use
• Changes in SystemStateTracker.cpp and LifecycleStates.cpp

Developer checklist (address before review)

• [ ] Changelog.md updated
• [ ] Prepared update for depending repositories
• [ ] Documentation updated (public API changes only)
• [ ] API docstrings updated (public API changes only)
• [ ] Rebase → commit history clean
• [ ] Squash and merge → proper PR title