Add signature messenger request serialization and processing

This update introduces a new serializer class for request messages (from messenger component). New features-includes encoding and decoding of request messages and handling unexpected value exceptions. A new test class for the serializer and it also adds functionality to process signature requests in the controller.

src/Bundle/ChillDocStoreBundle/Service/Signature/Driver/BaseSigner/RequestPdfSignMessage.php

@@ -0,0 +1,26 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * 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.
+ */
+
+namespace Chill\DocStoreBundle\Service\Signature\Driver\BaseSigner;
+
+use Chill\DocStoreBundle\Service\Signature\PDFSignatureZone;
+
+final readonly class RequestPdfSignMessage
+{
+    public function __construct(
+        public int $signatureId,
+        public PDFSignatureZone $PDFSignatureZone,
+        public int $signatureZoneIndex,
+        public string $reason,
+        public string $signerText,
+        public string $content,
+    ) {}
+}