feat: Environment Variable Provider

[MJRichardson]

Environment Variable Provider

This PR adds a provider that evaluates environment variables.

It will use the flag key as the name of the environment variable, but also provides the ability for a common prefix to be supplied when the provider is created.

            // If no prefix is required, the default constructor can be used, e.g.
            // var provider = new EnvVarProvider();
            var provider = new EnvVarProvider("FeatureToggles_");
            await OpenFeature.Api.Instance.SetProviderAsync(provider);

[beeme1mr]

Greetings @MJRichardson, could you please also update release-please-config.json? There's also seems to a lint issue.

Sorry for the delay on the review. Feel free to ping me if the PR get stuck again.

[askpt]

Looks good. I dropped a few minor suggestions. I advise you to run dotnet format in the repository's root to correct formatting errors.

[MJRichardson]

Greetings @MJRichardson, could you please also update release-please-config.json? There's also seems to a lint issue.

Sorry for the delay on the review. Feel free to ping me if the PR get stuck again.

Howdy @beeme1mr, and thanks :)

I've made those changes.

[beeme1mr]

Code looks good. I just left one comment about the readme. Thanks for the contribution!

[MJRichardson]

@beeme1mr While rebasing to sign my commits, I inadvertently signed commits which caused other reviewers to be added to the PR 🤦
I corrected this, but I can't remove the additional reviewers. Would you mind?

[beeme1mr]

Hey @MJRichardson, the provider is now available in NuGet. Thanks for the contribution!

https://www.nuget.org/packages/OpenFeature.Contrib.Providers.EnvVar