Use Windows APIs to do cryptography on Windows.

[teo-tsirpanis]

What component of google-cloud-cpp is this feature request for? common and storage

Is your feature request related to a problem? Please describe. The dependency to OpenSSL on Windows is problematic from a security perspective, because there is no standard way to update OpenSSL like Windows Update.

Describe the solution you'd like I would like that on Windows the client library do their cryptographic operations using Windows APIs, such as Cryptography API: Next Generation (CNG).

Describe alternatives you've considered N/A

Additional context If approved, I can work on this.