nixos/home-assistant: Wait for network-online.target

If people take the time to setup network-online.target correctly we
should wait for it. If they don't it's basically the same as
network.target anyway, so no harm done.

Over time I've seen multiple integrations that have dealt badly with
missing network connectivity at startup, this should alleviate further
pains.

nixos/modules/services/home-automation/home-assistant.nix

@@ -247,7 +247,7 @@ in {
 
     systemd.services.home-assistant = {
       description = "Home Assistant";
-      after = [ "network.target" ];
+      after = [ "network-online.target" ];
       preStart = optionalString (cfg.config != null) (if cfg.configWritable then ''
         cp --no-preserve=mode ${configFile} "${cfg.configDir}/configuration.yaml"
       '' else ''