Support requesting claims using actual claim identifiers

[kalegd]

Is your feature request related to a problem? Please describe.
As more credential formats come to exist, there will likely be claims that get missed by this library for a while. That would mean users can't request those claims at all without manually building the request themselves

Describe the solution you'd like
Allow users to specify claim identifiers in addition to or in lieu of our Claim enum

[kalegd]

One possible solution is to allow users to provide an object where the keys are the namespaces and the values are a list of claim ids under that namespace. Will need to consider if we should filter out those claims based on the DocumentTypes being requested. On the one hand, I think including namespaces that aren't accessible by those DocumentTypes doesn't make a difference as they won't be found, on the other hand it'll be cleaner to just apply them when relevant (as far as I can tell the namespace contained within the DocumentType string so that's an easy way to tell if it should be included for that DocumentType)