Add `ApiVersion` enum that can be injected into actuator endpoints if
they need to support more than one API revision.
Spring MVC, WebFlux and Jersey integrations now detect the API version
based on the HTTP accept header. If the request explicitly accepts a
`application/vnd.spring-boot.actuator.v` media type then the version
is set from the header. If no explicit Spring Boot media type is
accepted then the latest `ApiVersion` is assumed.
A new v3 API revision has also been introduced to allow upcoming health
endpoint format changes. By default all endpoints now consume and
can produce v3, v2 and `application/json` media types.
See gh-17929
deb9d67cef