Interfacing with environment variables

[cs-util]

Provide a simple interface that interacts with environment variables of the system (via EnvironmentV2 so that it can also be overridden for systems/operating systems that do not support the default implementation. Using these new methods create an IKeyValueStore so that a developer has this as a new option when choosing an IKeyValueStore implementation. Create a unit test that tests that the new IKeyValueStore is thread safe (might be possible to reuse one of the existing IKeyValueStore tests for this).

I will prepare a draft for this on a new branch that can be continued/completed.