[edit export] add required method on export's interface

The method "getFormDefaultData" is applyied on every interface which
will use it:

- ExportInterface
- AggregatorInterface
- DirectExportInterface
- FilterInterface

The method buildForm is moved to those interfaces.

[ci-skip]

src/Bundle/ChillMainBundle/Export/AggregatorInterface.php

@@ -12,6 +12,7 @@ declare(strict_types=1);
 namespace Chill\MainBundle\Export;
 
 use Closure;
+use Symfony\Component\Form\FormBuilderInterface;
 
 /**
  * Interface for Aggregators.
@@ -21,6 +22,16 @@ use Closure;
  */
 interface AggregatorInterface extends ModifierInterface
 {
+    /**
+     * Add a form to collect data from the user.
+     */
+    public function buildForm(FormBuilderInterface $builder);
+
+    /**
+     * Get the default data, that can be use as "data" for the form
+     */
+    public function getFormDefaultData(): array;
+
     /**
      * get a callable which will be able to transform the results into
      * viewable and understable string.