Configuration using environment variables doesn't allow setting namespace

[oyetteramirez]

Describe the bug

How do we set the namespace when configuring using environment variables?

I'm looking at this portion: https://github.com/MrZoidberg/VaultSharp.Extensions.Configuration/blob/master/Source/VaultSharp.Extensions.Configuration/VaultConfigurationExtensions.cs#L66, and it doesn't look like namespace is set from environment variables?

[MrZoidberg]

@oyetteramirez What's your use case for namespaces in environment variables?