Integrate documentation sources into model2owl repository and retire model2owl-docs

[gkostkowski]

The model2owl documentation has historically been maintained in a separate GitHub repository (model2owl-docs). However, it has been concluded that this setup provides no significant advantage and should be simplified by integrating the documentation sources directly into the model2owl repository.

The implementer is expected to:

• Remove the existing content of the docs directory in the model2owl repository.
• Transfer the documentation sources from model2owl-docs to the docs directory in the model2owl repository.
• Adapt the Antora configuration to work with the new documentation setup.
• Collaborate with the maintainer of the documentation service to ensure a smooth transition from the model2owl-docs repository to the documentation within the model2owl repository.

Note: Only the most recent version of the sources (3.0.0) will be migrated to the new location. As a result, earlier versions will no longer be available for publication. Nevertheless, their sources remain accessible in the archived repository.

Once the new setup is in place and verified to work, the model2owl-docs repository will be archived and no longer used.