add usage examples for conflate / conflate with seed (#25498)

* +doc conflate and conflateWithSeed docs examples

* fixes

* show throttle in the example so its more obvious that "slow upstream" etc

akka-docs/src/test/scala/docs/stream/operators/SourceOrFlow.scala

@@ -26,4 +26,30 @@ object SourceOrFlow {
     //#log
   }
 
+  def conflateExample(): Unit = {
+    //#conflate
+    import scala.concurrent.duration._
+
+    Source.cycle(() ⇒ List(1, 10, 100, 1000).iterator)
+      .throttle(10, per = 1.second) // faster upstream
+      .conflate((acc, el) ⇒ acc + el) // acc: Int, el: Int
+      .throttle(1, per = 1.second) // slow downstream
+    //#conflate
+  }
+
+  def conflateWithSeedExample(): Unit = {
+    //#conflateWithSeed
+    import scala.concurrent.duration._
+
+    case class Summed(i: Int) {
+      def sum(other: Summed) = Summed(this.i + other.i)
+    }
+
+    Source.cycle(() ⇒ List(1, 10, 100, 1000).iterator)
+      .throttle(10, per = 1.second) // faster upstream
+      .conflateWithSeed(el ⇒ Summed(el))((acc, el) ⇒ acc sum Summed(el)) // (Summed, Int) => Summed
+      .throttle(1, per = 1.second) // slow downstream
+    //#conflateWithSeed
+  }
+
 }