Fix enum generation for php-symfony generator (#14105)

* fix(symfony): enum generation

* docs(php symfony): update samples and docs

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/ApiResponse.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class ApiResponse 
 {
         /**

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Category.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class Category 
 {
         /**

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/EnumStringModel.php

@@ -41,15 +41,28 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
-class EnumStringModel 
+class EnumStringModel
 {
-        /**
-     * Constructor
-     * @param array|null $data Associated array of property values initializing the model
+    /**
+     * Possible values of this enum
      */
-    public function __construct(array $data = null)
+    const AVAILABLE = "available";
+    const PENDING = "pending";
+    const SOLD = "sold";
+    
+    /**
+     * Gets allowable values of the enum
+     * @return string[]
+     */
+    public static function getAllowableEnumValues()
     {
+        return [
+            self::AVAILABLE,
+            self::PENDING,
+            self::SOLD,
+        ];
     }
 }
 
 
+

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Order.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class Order 
 {
         /**

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Pet.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class Pet 
 {
         /**

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/Tag.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class Tag 
 {
         /**

samples/server/petstore/php-symfony/SymfonyBundle-php/Model/User.php

@@ -41,6 +41,7 @@ use JMS\Serializer\Annotation\SerializedName;
  * @package OpenAPI\Server\Model
  * @author  OpenAPI Generator team
  */
+
 class User 
 {
         /**