Add optional license key to provide in auth url callback

[tarecord]

When a user is redirected to a site to generate a token, there is no way to generate a token for a specific license key.

This adds an optional fluent method so uplink_callback includes a license key to which the auth site can register an associated token.

App::get( Auth_Url_Builder::class )->set_license( 'some-license-key' )->build( 'event-tickets', 'some-domain.com' );

[borkweb]

Glorious!