feat: Add support for passing addtl options to SPN Authentication

[laurayco]

currently there is no way to configure parameters in ClientSecretCredential. This is an issue if your application is behind a proxy and cannot dial out to Azure authentication servers without going through said proxy as the underlying @azure/* libraries do not respect typical (or any) environment variables ( ie: HTTP_PROXY / HTTPS_PROXY ). Other auth mechanisms similarly have equivalent functions and I am happy to include them here but wanted to confirm this would be allowed into the repo / understand feedback before digging into them as this is my first PR.