This commit adds an rfc for implementing a new providers interface. The
goal of this rfc is to document how we evolve the interface between
qiskit and providers moving forward to be something that is faster and
easier to work with.

Co-Authored-By: Thomas Alexander <thomasalexander2718@gmail.com>

A new Terra issue Qiskit/qiskit#4105 was opened that has partial
overlap with the work being done here. It had some good ideas that
would make the v2 interface a better fit for a world where there are
backends that do more than just run circuits (or pulse schedules). This
commit starts the process of integrating the ideas from that into the
larger refactor pending for the provider interface.

The job/result section was poorly worded and structured, leading to some
confusion about the intention to combine the 2 classes. This commit
updates the sdection to try and make it better written.

Between the PoC/WIP PR Qiskit/qiskit#4485
and recent review comments there has been a lot of feedback made on
the earlier versions of this RFC. This commit updates the RFC to take
much of that into account and also provide a clearer definition on some
aspects of the proposal.

Co-authored-by: Juan Gomez <atilag@gmail.com>

…rovider-interface