fix: #3336825 Implement hook_help()

David Suissarequested to merge
issue/ckeditor_details-3336825:3336825-hookhelp-is-missing-2.1.x into 2.1.x

https://www.drupal.org/project/ckeditor_details/issues/3336825

Initial implementation of hook_help based on the work in MR !3 by @elber and @Pracheth-SP.

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