r/z*2mqtt: Wait for clock to sync before starting

The *zwavejs2mqtt* and *zigbee2mqtt* services need to wait until the
system clock is fully synchronized before starting.  If the system clock
is wrong, they may fail to validate the MQTT server certificate.

The *time-sync.target* unit is not started until after services that
sync the clock, e.g. using NTP.  Notably, the *chrony-wait.service* unit
delays *time-sync.target* until `chrony waitsync` returns.

roles/zwavejs2mqtt/templates/zwavejs2mqtt.service.j2

@@ -1,7 +1,9 @@
 [Unit]
 Description=Zwavejs2Mqtt
 After=network-online.target
+After=time-sync.target
 Wants=network-online.target
+Wants=time-sync.target
 
 [Service]
 Type=notify