fix(hybrid): allow sending redirect_uri param to avoid redirect URI mismatch errors

[wJoenn]

closes #115

Summary

When using omniauth-apple with a API only Rails application it's common for the initial request to be made from the client side application instead of from Rails.
The client side application then receives a authorization code which it POST to /auth/apple/callback and the code is verified from the API before finally signing the user in.

When doing so the redirect_uri used in the callback process needs to be the same as the redirect_uri used in the request process so we need to be able to share that redirect_uri from the client side app to the API.

This is also the case with other omniauth-<provider> gem.

This PR allows sending a redirect_uri param to the /auth/apple/callback endpoint from a client side application and ensures that param will be used when present to avoid redirect uri mismatch errors.

---

Until this PR is merged this issue can be monkey patched by initializing a custom class that will override this gem

# config/initializers/omniauth-apple-monkey-patch.rb
module OmniAuth
  module Strategies
    class Apple
      def callback_url
        request.params['redirect_uri'] || options[:redirect_uri] || (full_host + callback_path)
      end
    end
  end
end