Consider removing or renaming Key trait's alias() method

[KendallWeihe]

Originally spurred here #204

What is the purpose of the .alias() method in the Key trait? Is it a unique digest? Whatever it is, we should probably rename the method.

It's unclear what the ideal design here is.

• Open question 1: it's a good point... the way I think about it is, the key alias is akin to a primary key in a db, so it's self referential with respect to a key. It's slightly confusing though because we enable callers of key manager methods to override the key alias, so it's a matter which is conceptualized at the key manager level, but at the same time we implement the alias for the Jwk which is the thumbprint. 🤔