Prior to this commit, the application availability infrastructure
would mix the `AvailabilityState`, the `HealthIndicator` and the
`HealthGroup` concepts and would not align with the rest.

This commit auto-configures the livenessState and readinessState
health indicators with the relevant configuration properties.
Unlike other indicators, they are not enabled by default but might
be in future versions.

This also moves the `management.health.probes.enabled` property
to `management.endpoint.health.probes.enabled` since "probes" here
is not a health indicator but rather a configuration flag for the
health endpoint.

Finally, the probes auto-configuration is refined to automatically
add liveness and readiness indicators for the probes group if
they're not already present.

Closes gh-22107