Deprecation message in PHP 8.2

Problem/Motivation

There's a deprecation notice emitted by the UserThirdpartyWrapper class on PHP 8.2

Deprecated function: Creation of dynamic property Drupal\autoshortqr\UserThirdpartyWrapper::$config is deprecated in Drupal\autoshortqr\UserThirdpartyWrapper->__construct()

> In PHP 8.2 and later, setting a value to an undeclared class property is deprecated, and emits a deprecation notice the first time the property is set during the lifetime of the application execution.

Proposed resolution

Should simply be a matter of initialising $config within the class