BUG: fixes for inventory management bugs

[ZLLentz]

Description

• Fix a bug where empty string or arbitrary command-line arguments would be used instead of the hostname during setup
• Fix a bug where empty host groups could not be added to
• Make sure this script will still work if we start using sub-element configuration in the inventory
• Make the type hinting for the _Inventory alias very verbose to help me fix the empty host groups

Motivation and Context

• The setup scripts are intended to add your PLC to the ansible inventory semi-automatically, only prompting for picking a group.
• Currently, this breaks down in several ways. See https://jira.slac.stanford.edu/browse/ECS-4976
• Continue using yaml directly rather than use the ansible config API because ansible says that their config file API should be considered internal/not public/not stable

How Has This Been Tested?

Interactively by adding hostnames to empty groups

Where Has This Been Documented?

Here + jira

Pre-merge checklist

• Code works interactively
• Code works interactively in dry_run mode
• Code contains descriptive docstrings, including context and API
• Pre-commit passes on GitHub Actions
• Documentation under https://confluence.slac.stanford.edu/display/PCDS/TcBSD has been updated appropriately

[tangkong]

All looks good to me. Still wrapping my head around all the bugs but this looks solid