Motivation:

When implementing a custom `HealthCheckUpdateHandler`, I just wanted to
add validation in front of the default implementation. However, it
wasn't possible because the default implementation has package-private
visibility.

Modifications:

- Expose the default `HealthCheckUpdateHandler` via `HealthCheckUpdateHandler.of()`

Result:

You can now use the default `HealthCheckUpdateHandler` via `HealthCheckUpdateHandler.of()`

…lthCheckUpdateHandler.java

Co-authored-by: minux <[email protected]>