Quickstarts: enable swagger

Read https://quarkus.io/guides/openapi-swaggerui

Requirements:

• On all quarkus quickstarts add something like quarkus-smallrye-openapi
• On the spring-boot quickstart add their variant of that module
• In both cases, add in the navbar of the index.html a link called "REST API" at the top right to the swagger generated REST api documentation.