Check for ability to integrate internal snippets

[maybeec]

Check for the internal snippets https://github.com/devonfw/.github/blob/master/CONTRIBUTING.asciidoc#documentation-changes by [.internal] markup.
Here the result: https://devonfw.com/website/pages/docs/contributing.asciidoc_using-github.html#contributing.asciidoc_documentation-changes

This mechanism must be available in antora as well.

It would be good when the current mechanism could be improved in a way that the placeholders are also not visible in the rendering of github. This would probably mean changing the placeholders to an asciidoc comment and converting them to the current solution before rendering them for the website.

[SchettlerKoehler]

• Check if syntax works
• Check if it is possible to include CSS and JS