Log health contributor status when overall eureka health status changed

[kzwang]

Is your feature request related to a problem? Please describe.
When 1 health contributor report it's DOWN, it will cause the overall eureka health status for that instance to be DOWN. If we look at the health actuator endpoint while the instance is DOWN, we can see which health contributor caused it to go down. However, if it recovered quickly, from logs we only know the instance changed from UP to DOWN, but we don't know which health contributor caused it unless there are logs or errors from that particular health contributor.

Describe the solution you'd like
We don't have to log the status of each health contributor for every health check, but if it caused a status change, it would be nice to log which one caused that change.

Describe alternatives you've considered
Make sure all health contributors log status changes, however, there are a lot of health contributors both from OSS in different projects, and internal ones, it's hard to make sure all health contributors have consistent logs.