Add actuator endpoint for exposing the Spring Integration graph

See gh-12331

spring-boot-project/spring-boot-docs/src/main/asciidoc/production-ready-features.adoc

@@ -105,6 +105,10 @@ exchanges).
 |Displays arbitrary application info.
 |Yes
 
+|`integrationgraph`
+|Exposes the Spring Integration graph.
+|No
+
 |`loggers`
 |Shows and modifies the configuration of loggers in the application.
 |Yes
@@ -252,6 +256,10 @@ endpoints:
 |Yes
 |Yes
 
+|`integrationgraph`
+|Yes
+|Yes
+
 |`jolokia`
 |N/A
 |No