Added interface to manage actions

Author: sebprt

src/ActionInterface.php

@@ -0,0 +1,8 @@
+<?php
+
+namespace Kiboko\Contract\Pipeline;
+
+interface ActionInterface
+{
+    public function execute(): iterable;
+}

src/ExecutingActionInterface.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Kiboko\Contract\Pipeline;
+
+interface ExecutingActionInterface
+{
+    public function execute(
+        ActionInterface $action,
+        RejectionInterface $rejection,
+        StateInterface $state
+    ): ExecutingActionInterface;
+}