Upgrade to Go JOSE v4

[hslatman]

What would you like to be added?

Upgrade to Go JOSE v4

Why this is needed

Tracking issue for upgrading this in due time. It was released in February 2024: https://github.com/go-jose/go-jose/releases/tag/v4.0.0.

There's no urgency right now, as v3 will be maintained for a bit, but it won't get new features:

Version 3, in this repo, is still receiving security fixes but not functionality updates.