Add content type

Author: Masiukevich Maksim

src/MessageEncoder.php

@@ -32,4 +32,9 @@ public function encode(object $message): string;
      * @throws \ServiceBus\MessageSerializer\Exceptions\NormalizationFailed Unexpected normalize result
      */
     public function normalize(object $message): array;
+
+    /**
+     * Receive encoded data content type.
+     */
+    public function contentType(): string;
 }

src/Symfony/SymfonySerializer.php

@@ -146,4 +146,9 @@ public function normalize(object $message): array
             throw new NormalizationFailed($throwable->getMessage(), (int) $throwable->getCode(), $throwable);
         }
     }
+
+    public function contentType(): string
+    {
+        return 'application/json';
+    }
 }