[Bug Report] Behaviour of enforce_dependencies: key missing

Description
Without enforce_dependencies: present in a package config, it is assumed that dependency enforcement is false. I think this is a bug because the key should be required. You can turn off dependency enforcement if you want, but the package YAML should explicitly do so. It makes it easier to turn on later, and to have a more readable config file.

Since dependency enforcement is Packwerk's only flagship check now, I don't know why you wouldn't want to use it eventually.

To Reproduce
Create a package.yml without enforce_dependencies and run bin/packwerk validate. This passes, and Packwerk registers this as being disabled / false.

Expected Behaviour
Validation fails and asks for the ket to exist, or the default is true.

Screenshots
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Version Information

• Packwerk: 3.0 / edge
• Ruby 3.2.1

Additional Context
I think we want to make the key required. It makes the most sense to me. All checker keys should likely be made required.

Start with the package.yml configuration handling reached by bin/packwerk validate, and run the reproduction with enforce_dependencies omitted. Check the existing validation behavior and tests, if present. Done means validation consistently rejects a missing key or applies the agreed true default, with coverage for the missing-key case.