chore: Increase initial delay to show loading indicator (#14984)

The current initial delay to show loading indicator seems quite short. If one deploys an app to another continent, even no op visits can make the indicator "flash". This may kind of just increases the feeling of "broken app". Especially as the indicator in latest versions is bold visually.

Still, at least mine app feels perfectly usable and don't even realise there is a server visit. I don't have the skills to me the indication look less bolder, so I'd just propose to increase the delay a bit. With this level (450ms) all seems to work fine.

flow-server/src/main/java/com/vaadin/flow/internal/nodefeature/LoadingIndicatorConfigurationMap.java

@@ -29,7 +29,7 @@
 public class LoadingIndicatorConfigurationMap extends NodeMap
         implements LoadingIndicatorConfiguration {
     public static final String FIRST_DELAY_KEY = "first";
-    public static final int FIRST_DELAY_DEFAULT = 300;
+    public static final int FIRST_DELAY_DEFAULT = 450;
     public static final String SECOND_DELAY_KEY = "second";
     public static final int SECOND_DELAY_DEFAULT = 1500;
     public static final String THIRD_DELAY_KEY = "third";