fix: set load-on-startup for automatically registered Vaadin servlet (#…

…398) (#410)

When using Vite, DevModeInitializer blocks dev-server startup until a
VaadinServlet is deployed because it needs to get the servlet path to use.
If the container lazily loads servlets, Vite will not start until the first
HTTP request for the Vaadin servlet is received.
This change sets load-on-startup feature for automatically deployed Vaadin
servlet, to ensure that the servlet and Vite are loaded on the startup of the
Web application

Part of vaadin/flow#14479

Co-authored-by: Marco Collovati <[email protected]>

vaadin-cdi/src/main/java/com/vaadin/cdi/CdiServletDeployer.java

@@ -85,6 +85,7 @@ public void onStartup(Set<Class<?>> classSet, ServletContext ctx) {
 
         registration.setAsyncSupported(true);
         registration.addMapping("/*");
+        registration.setLoadOnStartup(1);
     }
 
     private static ServletRegistration findRootServlet(ServletContext context) {