Allow custom health check status mapping

With Spring Boot Actuator health check endpoint, we can use management.endpoint.health.status.http-mapping.<status> to map a custom status to an HTTP status code. But for Eureka integration, any custom status would map to UNKNOWN status in Eureka since the mapping is not configurable (https://github.com/spring-cloud/spring-cloud-netflix/blob/master/spring-cloud-netflix-eureka-client/src/main/java/org/springframework/cloud/netflix/eureka/EurekaHealthCheckHandler.java#L61-L64). It would be nice if we can map custom statuses to UP/DOWN/OUT_OF_SERVICE via properties similar to the health check endpoint HTTP status mapping.