#22903 Fix code snippeds

* move scala and java sources out of paradox sources
* replace relative paths with $code$ and $akka$
* fix broken includes

akka-docs/src/main/scala/docs/stream/cookbook/RecipeFlattenSeq.scala

@@ -0,0 +1,29 @@
+package docs.stream.cookbook
+
+import akka.NotUsed
+import akka.stream.scaladsl.{ Sink, Source }
+
+import scala.collection.immutable
+import scala.concurrent.Await
+import scala.concurrent.duration._
+
+class RecipeFlattenSeq extends RecipeSpec {
+
+  "Recipe for flatteing a stream of seqs" must {
+
+    "work" in {
+
+      val someDataSource = Source(List(List("1"), List("2"), List("3", "4", "5"), List("6", "7")))
+
+      //#flattening-seqs
+      val myData: Source[List[Message], NotUsed] = someDataSource
+      val flattened: Source[Message, NotUsed] = myData.mapConcat(identity)
+      //#flattening-seqs
+
+      Await.result(flattened.limit(8).runWith(Sink.seq), 3.seconds) should be(List("1", "2", "3", "4", "5", "6", "7"))
+
+    }
+
+  }
+
+}