add example to the doc of combine operator (#30194)

akka-docs/src/main/paradox/stream/operators/Sink/combine.md

@@ -6,12 +6,29 @@ Combine several sinks into one using a user specified strategy
 
 ## Signature
 
-@apidoc[Sink.combine](Sink$) { scala="#combine[T,U](first:akka.stream.scaladsl.Sink[U,_],second:akka.stream.scaladsl.Sink[U,_],rest:akka.stream.scaladsl.Sink[U,_]*)(strategy:Int=>akka.stream.Graph[akka.stream.UniformFanOutShape[T,U],akka.NotUsed]):akka.stream.scaladsl.Sink[T,akka.NotUsed]" java="#combine(akka.stream.javadsl.Sink,akka.stream.javadsl.Sink,java.util.List,akka.japi.function.Function)" }
+@apidoc[Sink.combine](Sink$) { scala="
+#combine[T,U](first:akka.stream.scaladsl.Sink[U,_],second:akka.stream.scaladsl.Sink[U,_],rest:akka.stream.scaladsl.Sink[U,_]*)(
+strategy:Int=>akka.stream.Graph[akka.stream.UniformFanOutShape[T,U],akka.NotUsed]):
+akka.stream.scaladsl.Sink[T,akka.NotUsed]" java="#combine(
+akka.stream.javadsl.Sink,akka.stream.javadsl.Sink,java.util.List,akka.japi.function.Function)" }
 
 ## Description
 
 Combine several sinks into one using a user specified strategy
 
+## Example
+
+This example shows how to combine multiple sinks with a Fan-out Junction.
+
+Scala
+:
+@@snip [StreamPartialGraphDSLDocSpec.scala](/akka-docs/src/test/scala/docs/stream/StreamPartialGraphDSLDocSpec.scala) {
+#sink-combine }
+
+Java
+:   @@snip [StreamPartialGraphDSLDocTest.java](/akka-docs/src/test/java/jdocs/stream/StreamPartialGraphDSLDocTest.java)
+{ #sink-combine }
+
 ## Reactive Streams semantics
 
 @@@div { .callout }