Feature/multi file pg

[Jonesy]

Description

This feature branch brings the new codebase at parity with the original $ gwa pg command which would

1. Allow you to define multiple inputs
2. Allow you to not enter an input argument and instead grab all the CWD's config files and merge them as a single one.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Documentation (non-breaking change with enhancements to documentation)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have checked that unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

As a side-note I added experimental Nix flake support so when using Nix a developer could run $ nix develop to pull all the Go and Just dependencies and run it in a containerized shell. If there's any concerns about using it let me know and I'll pull it. You can read more about it here https://nixos.org/manual/nix/stable/command-ref/new-cli/nix3-develop.html