Changes for the nats chart:

Breaking

The podManagementPolicy value was introduced and set to Parallel by default, which controls the StatefulSet spec.podManagementPolicy field. This field is immutable and cannot be changed on an existing StatefulSet; to upgrade from an older chart version, add the value:
```
podManagementPolicy: OrderedReady
```

Introduces using /healthz as a startup check when the image version is 2.7.1 during upgrades
The preStop command no longer waits for terminationGracePeriodSeconds since this blocks pod termination, this workaround used to exist for when nats-server did not handle TERM but since v2.2 it does now so lame duck should work correctly without being stopped prematurely.
podManagementPolicy is now set to Parallel by default .
readiness probe is disabled now by default (it was the same as livenessProbe and the startupProbe covers the same check during startup now)

In case have to disable the startup check, then can do the following:

nats:
  healthcheck:
    startup:
      enabled: false