Renderers should display example changes, not just schema changes

[DrSatyr]

When a ChangedMediaType has example changes but no schema changes, the renderers (Console, Markdown, Asciidoc, HTML) currently show nothing in the details section because they only render schema changes. The ChangedMediaType model has example and examples fields that could be rendered alongside schema changes.

This was discovered while fixing https://github.com/OpenAPITools/openapi-diff/issues/870 where the NPE was caused by null schema when only examples changed.