[backup-client] Compile to wasm

Summary:
Compiles backup client to WASM for web. Uses a similar approach to SQliteQueryExecutor where we keep the files inside of the git repository.

• tokio-tungstenite-wam allows us to have one API for native (tungstenite) and web websockets. It has very similar API to tungstenite but required a few small changes that I will annotate
• web.rs contains a wasm-only file providing JS<->Rust conversions and helpers
• A few structs got either serde implementations or conditional wasm_bindgen attributes so that they are available in JS or can be deserialized as arguments from JS

Adding @ashoat as reviewer because of dependency changes.

Depends on D11040

Test Plan:

• Check that native still compiles (both Android and iOS)
• Check that compiling to WASM works (yarn build)
• Testing that backup client in WASM works is tested in the future diffs

Reviewers: marcin, bartek, kamil, ashoat

Reviewed By: kamil, ashoat

Subscribers: atul, tomek, ashoat

Differential Revision: https://phab.comm.dev/D11041