INT-4458: Do not expose recursive generics API (#2432)

* INT-4458: Do not expose recursive generics API

JIRA: https://jira.spring.io/browse/INT-4458

According Kotlin generics system restrictions we can't expose API
based on the recursive generics, like we have with Java DSL for JMS

* Replace explicit recursive generics on factory method with the wildcard (`?`).
This way both Kotlin and Java are able to instantiate target object and perform
the proper chain API auto-completion
* Fix `JmsInboundChannelAdapterSpec` to deal with provided `S` type for the
`configureListenerContainer()` - the way we can configure a `JmsDefaultListenerContainerSpec`
* Add `kotlin-spring` Gradle plugin to avoid extra `open` modificator on `@Bean` methods
* Add `JmsDslKotlinTests.kt`

**Cherry-pick to 5.0.x excluding Kotlin support**

* Fix `Amqp` DSL factory for recursive generics

* Polishing for Kotlin tests

spring-integration-core/src/test/kotlin/org/springframework/integration/dsl/routers/RouterDslTests.kt

@@ -68,10 +68,10 @@ class RouterDslTests {
 
     @Configuration
     @EnableIntegration
-    open class Config {
+    class Config {
 
         @Bean
-        open fun routerTwoSubFlows() =
+        fun routerTwoSubFlows() =
                 IntegrationFlow { f ->
                     f.split()
                             .route<Int, Boolean>({ p -> p % 2 == 0 },