Create axum variant for wasm (no Tokio)

[zeeshanlakhani]

Summary

As of 0.6, axum supports being compiled to WebAssembly by disabling the tokio feature. We can support a serverless runtime for single requests/responses, e.g. https://github.com/tokio-rs/axum/blob/main/examples/simple-router-wasm/src/main.rs.

Need to mainly look into how extended functionality w/ tracing, metrics, holds up or which parts need to be discarded.