Add config schema

Currently, it's not possible to translate the templates because the configuration is not translatable.

As mentioned in https://www.drupal.org/project/projectownership/issues/3512466 💬 Is node form templates still being maintained? Needs work , Naveko is looking into it.

The merge requests have been accepted and I tested the code. Nodes created with node templates can now be translated, so I'm marking this issue 'Fixed'.