Ability for deck diff to differentiate differences

Is it possible for deck diff to differentiate between:

- If a config value is present in a workspace configuration file but not Kong
- If a config value is not present in a workspace configuration file but in Kong

Currently for both scenarios, deck diff will return an exit code of 2. This isn't useful if we want to use deck diff in a CICD pipeline if we want to fail the build if a developer has forgot to add config to a workspace configuration file but has manually added the setting in the UI. I want to add this check to ensure we don't lose settings added via the UI when running a deck sync if a configuration value hasn't been added to a configuration file in source control.

Start by tracing deck diff's comparison and exit-code handling for workspace configuration versus Kong state. Define distinct results for settings present only in the workspace and settings present only in Kong, then verify that CI/CD users can distinguish these outcomes without losing UI-managed settings during a later deck sync.

Written by the indexing model from the issue text.