Introduce attribute support in Kotlin RouterFunction DSL

[christophejan]

On current spring framework version (5.3.19), RouterFunction attributes are not supported by RouterFunction Kotlin DSL.

RouterFunction attributes is currently supported by Java Builder :

• spring-framework/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RouterFunctionBuilder.java

  Line 335 in 172102d

  public RouterFunctions.Builder withAttribute(String name, Object value) {

• spring-framework/spring-webflux/src/main/java/org/springframework/web/reactive/function/server/RouterFunctionBuilder.java

  Line 350 in 172102d

  public RouterFunctions.Builder withAttributes(Consumer<Map<String, Object>> attributesConsumer) {

• spring-framework/spring-webmvc/src/main/java/org/springframework/web/servlet/function/RouterFunctionBuilder.java

  Line 328 in 172102d

  public RouterFunctions.Builder withAttribute(String name, Object value) {

• spring-framework/spring-webmvc/src/main/java/org/springframework/web/servlet/function/RouterFunctionBuilder.java

  Line 343 in 172102d

  public RouterFunctions.Builder withAttributes(Consumer<Map<String, Object>> attributesConsumer) {

But RouterFunction attributes support is missing from all Kotlin DSL :

• spring-framework/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/RouterFunctionDsl.kt

  Line 65 in 172102d

  class RouterFunctionDsl internal constructor (private val init: RouterFunctionDsl.() -> Unit) {

• spring-framework/spring-webflux/src/main/kotlin/org/springframework/web/reactive/function/server/CoRouterFunctionDsl.kt

  Line 66 in 172102d

  class CoRouterFunctionDsl internal constructor (private val init: (CoRouterFunctionDsl.() -> Unit)) {

• spring-framework/spring-webmvc/src/main/kotlin/org/springframework/web/servlet/function/RouterFunctionDsl.kt

  Line 62 in 172102d

  class RouterFunctionDsl internal constructor (private val init: (RouterFunctionDsl.() -> Unit)) {