Clarify that Kotlin DSL needs an import

Closes gh-13092

docs/modules/ROOT/pages/servlet/configuration/kotlin.adoc

@@ -16,6 +16,8 @@ It is configured with the following default implementation:
 
 [source,kotlin]
 ----
+import org.springframework.security.config.annotation.web.invoke
+
 @Bean
 open fun filterChain(http: HttpSecurity): SecurityFilterChain {
    http {
@@ -29,6 +31,9 @@ open fun filterChain(http: HttpSecurity): SecurityFilterChain {
 }
 ----
 
+[NOTE]
+Make sure that import the `invoke` function in your class, sometimes the IDE will not auto-import it causing compilation issues.
+
 The default configuration above:
 
 * Ensures that any request to our application requires the user to be authenticated
@@ -54,6 +59,8 @@ For example, the following is an example of having a different configuration for
 
 [source,kotlin]
 ----
+import org.springframework.security.config.annotation.web.invoke
+
 @EnableWebSecurity
 class MultiHttpSecurityConfig {
     @Bean                                                            <1>