Add BC fo AuthenticationPluginInterface::getAuthenticationOptions params added in CS update

Problem/Motivation

\Drupal\migrate_plus\AuthenticationPluginInterface::getAuthenticationOptions introduced new parameters in a minor.

The problem should have been resolved in a different way, there are ways to introduce new parameters without breaking existing code.

This parameter could have been nullable, while migrate_plus also set the value of the parameter with an internal instance method. There would be temporary duplication, but it would solve issues like this. I'm sure there are other ways to handle this, of course.