Feature: Investigate WASM/WASI targets

[sjrusso8]

Description

Being able to compile the rust bindings into wasm32-unknown-unknown and/or wasm32-wasi would be interesting. This could allow some interesting interactions between a browser and spark. A wasm32-wasi target would allow spark programs to run on any runtime.

Early Experiments

A feature flag under the core bindings for wasm already exists and does compile successfully to those targets mentioned above. The issue arises when trying to send a HTTP1.1 request with grpc-web to the Spark Connect server, which only accepts normal HTTP2 grpc requests. There are methods of standing up a proxy server with envoy to forward the gRPC browser request to the backend server. But this feels like a lot of effort for the client to do.

The branch feat/wasm contains the early experiment and trying to run wasm with wasmtime. Issue arises with using async code in wasm. There is probably a way to code it correctly, but I don't have time to finish the experiment

[sjrusso8]

Was able to create a wasm program to run a simple spark structure streaming job. The brach feat/wasm was updated with envoy to handle the grpc-web requests. Might consider having an 'example' section for how to setup envoy and use the wasm feature flag.