feat: Add new StoredObjectManager service.

To read and write onto `StoredObject` document using a common interface.

src/Bundle/ChillDocStoreBundle/Service/StoredObjectManagerInterface.php

@@ -0,0 +1,34 @@
+<?php
+
+/**
+ * Chill is a software for social workers
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+declare(strict_types=1);
+
+namespace Chill\DocStoreBundle\Service;
+
+use Chill\DocStoreBundle\Entity\StoredObject;
+
+interface StoredObjectManagerInterface
+{
+    /**
+     * Get the content of a StoredObject.
+     *
+     * @param StoredObject $document The document.
+     *
+     * @return string The retrieved content in clear.
+     */
+    public function read(StoredObject $document): string;
+
+    /**
+     * Set the content of a StoredObject.
+     *
+     * @param StoredObject $document The document.
+     * @param $clearContent The content to store in clear.
+     */
+    public function write(StoredObject $document, string $clearContent): void;
+}