Provide custom BackgroundExecutorWrapper to pass thread locals

(cherry picked from commit 336accf447)

ebean-api/src/main/java/io/ebean/config/BackgroundExecutorWrapper.java

@@ -0,0 +1,23 @@
+package io.ebean.config;
+
+import java.util.concurrent.Callable;
+
+/**
+ * BackgroundExecutorWrapper that can be used to wrap tasks that are sent to background (i.e. an other thread).
+ * It should copy all neccessary thread-local variables. See {@link MdcBackgroundExecutorWrapper} for implementation details.
+ * 
+ * @author Roland Praml, FOCONIS AG
+ */
+public interface BackgroundExecutorWrapper {
+
+  /**
+   * Wrap the task with MDC context if defined.
+   */
+  <T> Callable<T> wrap(Callable<T> task);
+
+  /**
+   * Wrap the task with MDC context if defined.
+   */
+  Runnable wrap(Runnable task);
+
+}