When the gokrazy deployment doesn't have internet access and the network
lacks NTP traffic re-routing to the local time servers, instances may
either have downright wrong clock (e.g. Raspberry Pi with no RTC) or
experience divergence due to drift.
This add the ability to override the default NTP Pool Vendor Zone for
gokrazy with servers supplied as command line arguments.
e.g.
```
"PackageConfig": {
"github.com/gokrazy/gokrazy/cmd/ntp": {
"CommandLineFlags": [
"time1.local",
"time2.local",
"10.1.2.123"
]
}
}
```
Ami Fischman
Berk D. Demir
Michael Stapelberg