add wstd-azure crate

[cataggar]

Create a wstd-azure crate following a structure similar to the wstd-aws crate:

• add wstd-aws crate, for integration with aws-sdk bytecodealliance/wstd#102

There are two extension points that need to be implemented:

• azure_core::async_runtime::AsyncRuntime
  documented at https://docs.rs/azure_core/latest/azure_core/async_runtime/trait.AsyncRuntime.html
• azure_core::http::HttpClient
  documented at https://docs.rs/azure_core/latest/azure_core/http/trait.HttpClient.html

I created a working example of implementing both using the Spin SDK in

• experiment to add support for wasm32-wasip2 using Spin Azure/azure-sdk-for-rust#2974

Instead of the Spin SDK, use wstd.