Update the `HealthEndpoint` to support health groups. The
`HealthEndpointSettings` interface has been replaced with
`HealthEndpointGroups` which provides access to the primary group
as well as an optional set of additional groups.

Groups can be configured via properties and may have custom
`StatusAggregator` and `HttpCodeStatusMapper` settings.

Closes gh-14022
Co-authored-by: Stephane Nicoll <snicoll@pivotal.io>