fix: feature to allow switching to rustls

[tomtau]

Description

allow switching to rustls in tokio-tungstenite: we find rustls to be more portable, so we prefer using that

Resolves # N/A #9

How Has This Been Tested?

using cargo run --example basic_client --features full, plus a custom partial Sign API implementation

Due Diligence

• Breaking change
• Requires a documentation update
• Requires a e2e/integration test update

[heilhead]

Thanks! I've replaced it with #12 to also update our CI workflow to run cocogitto to verify commits, and update the commit message.