clean up logged error messages

Added a null coalesce on $state['mfaLearnMoreUrl'] for the review page
- fixes error: SimpleSAML\Error\Exception: Warning - Undefined array key "mfaLearnMoreUrl" at /data/vendor/simplesamlphp/simplesamlphp/modules/profilereview/public/nag.php:37
Defined exampleauth:UserPass users in users key
- fixes error: Module exampleauth:UserPass configured in legacy mode. Please put your username:password entries under the "users" key in your authsource.
Changed from if to assert to catch error condition earlier
Stop using the admin module to access the hub discovery page
- fixes error: Caused by: Twig\Error\RuntimeError: An exception has been thrown during the rendering of a template ("SimpleSAML\XHTML\Template::getEntityDisplayName(): Argument #1 ($data) must be of type array, null given, called in /data/vendor/twig/twig/src/Environment.php(392) : eval()'d code on line 82").
Filled in missing data in authsources.php
- fixes error: SimpleSAML\Error\Exception: Warning - Undefined array key "add" at /data/vendor/simplesamlphp/simplesamlphp/modules/profilereview/src/Auth/Process/ProfileReview.php:234

silinternational / ssp-base