Consider bringing back ring

[gtrak]

I didn't want to necro #454, but this is a continuation of that thread.

Aws-lc is actually broken for us, and others that use cargo-zigbuild, and cross-compilation is also more difficult due to the jitterentropy library:
aws/aws-lc#2733
aws/aws-lc-rs#680
aws/aws-lc-rs#512
aws/aws-lc-rs#912

I don't have an argument against using rust-crypto yet, but why not bring back ring as a build-time feature? A lot of things still depend on it. Ureq->rustls->ring still is in our dep tree. The ring repo seems pretty active lately, too.

[Keats]

The idea is to allow something like #452 rather than have all the backends in that crate. I'm not planning to adding any more backends in this crate, once there is a trait people can create jsonwebtoken-ring if they want to.

A lot of things still depend on it. Ureq->rustls->ring still is in our dep tree.

rustls defaults to aws-lc-rs so it's just ureq using their ring feature