Provide patterns and infrastructure for assigning remote identifiers (DOI, Handle, etc.)

[cjcolvar]

There are three patterns provided: dispatcher, registrar, and builder
Dispatcher - assigns registered identifier to a given object
Registrar - handles communication with external identifier service
Builder - constructs identifier to submit to external identifier service

Registrar implementations just need to implement the registrar!
method. They can be tested with the provided shared spec and then
registered with Hyrax by the identifier_registrars configuration (which
is generated commented out in the hyrax initializer).
identifier_registrars should be a Hash with Symbol keys and Class values.

A custom builder implementation can be injected into your registrar by
overriding the registrar's initialize method setting the custom builder
as the default value for the builder keyword argument.

def initialize(builder: MyCustomBuilder.new)
  super(builder: builder)
end

With this infrastructure in place, a new remote identifier can be
assigned to a work by calling the dispatcher with the work object.
Assuming a :datacite registrar has been registered in Hyrax's
configuration then this would look like:

Hyrax::Identifier::Dispatcher.for(:datacite).assign_for!(object: work)

This will set the remote identifier in the work's identifier attribute
and save the work. To avoid saving the object use assign_for instead.
If a different attribute is desired the pass the attribute as a symbol
in the :attribute keyword argument to assign_for!.

This work is ported from mahonia (which had parts ported from epigaea).
Both of those implementations were done by @no-reply.

This is a slightly simpler and less opinionated alternative to hydra-remote_identifier. The mapping of work attributes to metadata submitted to the identifier registration service is left up to the registrar implementation here instead of being configured like in hydra-remote_identifier.

@samvera/hyrax-code-reviewers

[no-reply]

this seems great to me!

since it's basically a straight port of code i wrote, i'd like to see someone else review. but i'm chiming in to offer my 👍.