refactor: documents interfaces

Signed-off-by: Sebastian Krupinski <krupinski01@gmail.com>

shared/lib/Documents/Collection/CollectionContent.php

@@ -0,0 +1,23 @@
+<?php
+
+declare(strict_types=1);
+
+/**
+ * SPDX-FileCopyrightText: Sebastian Krupinski <krupinski01@gmail.com>
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace KTXF\Documents\Collection;
+
+use JsonSerializable;
+
+enum CollectionContent: string implements JsonSerializable {
+
+    case File = 'file';
+    case Folder = 'folder';
+
+    public function jsonSerialize(): string {
+        return $this->value;
+    }
+
+}