fix: added missing main class to SpringApplicationBuilder (#1580)

fix: replaced `AnnotationConfigServletWebServerApplicationContext` with `ConfigurableWebApplicationContext` (#1580)

Author: andreossido

aws-serverless-java-container-springboot3/src/main/java/com/amazonaws/serverless/proxy/spring/SpringBootLambdaContainerHandler.java

@@ -18,7 +18,7 @@
 import org.slf4j.LoggerFactory;
 import org.springframework.boot.WebApplicationType;
 import org.springframework.boot.builder.SpringApplicationBuilder;
-import org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext;
+import org.springframework.web.context.ConfigurableWebApplicationContext;
 import org.springframework.context.ConfigurableApplicationContext;
 
 import com.amazonaws.serverless.exceptions.ContainerInitializationException;
@@ -192,12 +192,15 @@ public void initialize()
 
         SpringApplicationBuilder builder = new SpringApplicationBuilder(getEmbeddedContainerClasses())
                 .web(springWebApplicationType); // .REACTIVE, .SERVLET
+        if(springBootInitializer != null) {
+            builder.main(springBootInitializer);
+        }
         if (springProfiles != null) {
             builder.profiles(springProfiles);
         }
         applicationContext = builder.run();
         if (springWebApplicationType == WebApplicationType.SERVLET) {
-            ((AnnotationConfigServletWebServerApplicationContext)applicationContext).setServletContext(getServletContext());
+            ((ConfigurableWebApplicationContext)applicationContext).setServletContext(getServletContext());
             AwsServletRegistration reg = (AwsServletRegistration)getServletContext().getServletRegistration(DISPATCHER_SERVLET_REGISTRATION_NAME);
             if (reg != null) {
                 reg.setLoadOnStartup(1);