Clarify that Kotlin DSL needs an import

Closes gh-13092

docs/modules/ROOT/pages/reactive/configuration/webflux.adoc

@@ -94,6 +94,8 @@ public class HelloWebfluxSecurityConfig {
 .Kotlin
 [source,kotlin,role="secondary"]
 -----
+import org.springframework.security.config.web.server.invoke
+
 @Configuration
 @EnableWebFluxSecurity
 class HelloWebfluxSecurityConfig {
@@ -122,6 +124,9 @@ class HelloWebfluxSecurityConfig {
 -----
 ====
 
+[NOTE]
+Make sure that you import the `invoke` function in your Kotlin class, sometimes the IDE will not auto-import it causing compilation issues.
+
 This configuration explicitly sets up all the same things as our minimal configuration.
 From here you can easily make the changes to the defaults.
 
@@ -176,6 +181,8 @@ static class MultiSecurityHttpConfig {
 .Kotlin
 [source,kotlin,role="secondary"]
 ----
+import org.springframework.security.config.web.server.invoke
+
 @Configuration
 @EnableWebFluxSecurity
 open class MultiSecurityHttpConfig {

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>