Add XML and YAML DTOs config examples (#790)

* Add XML and YAML DTOs config examples

* Update core/dto.md

Co-Authored-By: jbdelhommeau <[email protected]>

* Update dto.md

Author: jbdelhommeau

core/dto.md

@@ -26,6 +26,34 @@ final class Book
 }
 ```
 
+Or using XML:
+
+```xml
+<?xml version="1.0" encoding="UTF-8" ?>
+<!-- api/config/api_platform/resources.xml -->
+
+<resources xmlns="https://api-platform.com/schema/metadata"
+           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+           xsi:schemaLocation="https://api-platform.com/schema/metadata
+           https://api-platform.com/schema/metadata/metadata-2.0.xsd">
+    <resource class="App\Entity\Book">
+      <attribute name="input">App\Dto\BookInput</attribute>
+      <attribute name="output">App\Dto\BookOutput</attribute>
+    </resource>
+</resources>
+```
+
+Or using YAML:
+
+```yaml
+# api/config/api_platform/resources.yaml
+resources:
+    App\Entity\Book:
+        attributes:
+            input: App\Dto\BookInput
+            output: App\Dto\BookOutput
+```
+
 The `input` attribute is used during [the deserialization process](serialization.md), when transforming the user-provided data to a resource instance.
 Similarly, the `output` attribute is used during [the serialization process](serialization.md). This class represents how the `Book` resource will be represented in the `Response`.