feat: separate DID Method trait from Create trait for create-able DIDs

[enmand]

Some DID methods allow for DID creation (e.g. with some key pair) and some have more infrastructure requirements around them (like did:web). This PR separates the trait for "create-able" DIDs, so that DID methods like did:web don't have to carry around trait types and no-implementation-implementations for trait functions they don't need.

[enmand]

On second though, maybe there is value in having all the methods defined in a single trait, even if it's a bit cumbersome for some method implementations -- I could see a world where there are separate e.g. Resolve, Create, Update and Deactivate trait but I also see value in having all the methods under a single trait

[KendallWeihe]

I'm a little torn on this and need to think about it. I think it's a great idea to come to an implementation wherein the lack of support of a feature is determinable at build-time, as opposed to how we currently have things which wouldn't be discovered until runtime. However, strictly aligning to the specification I view all of the various CRUD operations on a method as a bundle of features and so at face value it makes sense for them to be in a single trait. I think... probably what you have proposed here @enmand is ideal, but let's let it sit for a bit and we can contemplate 🤔

[KendallWeihe]

let's do it!