#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/java/jdocs/stream/Main.java

@@ -0,0 +1,9 @@
+package jdocs.stream;
+
+//#main-app
+public class Main {
+  public static void main(String[] argv) {
+    // Code here
+  }
+}
+//#main-app