add option to use async friendly datastore

[sriv]

this comes as a property because I could not find a way to detect this automagically

[gaugebot]

@sriv Thank you for contributing to gauge-csharp-lib. Your pull request has been labeled as a release candidate 🎉🎉.

Merging this PR will trigger a release.

Please bump up the version as part of this PR.

Instructions to bump the version can found at CONTRIBUTING.md

If the CONTRIBUTING.md file does not exist or does not include instructions about bumping up the version, please looks previous commits in git history to see what changes need to be done.

[mpekurny]

Will this work with multithreaded runs? Since this is switching it from a thread local to a static value, all threads would access the same dictionary. If multiple steps/scenario/specs are running, they would all access the same data store, correct?

[chadlwilson]

Believe this isn't required now as there is an alternate solution proposed and merged in #45, so will close this for now?