Add showcase list page

via [Discussion](https://meta.answer.dev/questions/D1343/showcase-of-production-answer-examples):

Add a [showcase page](https://www.figma.com/design/5nxbSDjPTlH1Uw8tYhFuiA/Apache-Answer-Website?node-id=3184-568&t=k3rjpQMBKQXdvizk-4) on the official website to provide a more intuitive view of the actual use cases of Apache Answer.