+str #15750 Prototype of stream supervision

* add supervion for stages and built in ops run by interpreter
* add supervision for mapAsync and mapAsyncUnordered
* add supervision to groupBy and splitWhen
* reference doc for scala and java

akka-docs-dev/rst/scala/code/docs/stream/IntegrationDocSpec.scala

@@ -22,6 +22,7 @@ import akka.stream.scaladsl.OperationAttributes
 import scala.concurrent.ExecutionContext
 import akka.stream.ActorFlowMaterializerSettings
 import java.util.concurrent.atomic.AtomicInteger
+import akka.stream.Supervision
 
 object IntegrationDocSpec {
   import TwitterStreamQuickstartDocSpec._
@@ -52,6 +53,13 @@ object IntegrationDocSpec {
       Future.successful(Some(handle.hashCode.toString))
   }
 
+  class AddressSystem2 {
+    //#email-address-lookup2
+    def lookupEmail(handle: String): Future[String] =
+      //#email-address-lookup2
+      Future.successful(handle + "@somewhere.com")
+  }
+
   final case class Email(to: String, title: String, body: String)
   final case class TextMessage(to: String, body: String)
 
@@ -159,6 +167,22 @@ class IntegrationDocSpec extends AkkaSpec(IntegrationDocSpec.config) {
     probe.expectMsg("akkateam@somewhere.com")
   }
 
+  "lookup email with mapAsync and supervision" in {
+    val addressSystem = new AddressSystem2
+    val authors: Source[Author] =
+      tweets.filter(_.hashtags.contains(akka)).map(_.author)
+
+    //#email-addresses-mapAsync-supervision
+    import OperationAttributes.supervisionStrategy
+    import Supervision.resumingDecider
+
+    val emailAddresses: Source[String] =
+      authors.section(supervisionStrategy(resumingDecider)) {
+        _.mapAsync(author => addressSystem.lookupEmail(author.handle))
+      }
+    //#email-addresses-mapAsync-supervision
+  }
+
   "calling external service with mapAsyncUnordered" in {
     val probe = TestProbe()
     val addressSystem = new AddressSystem