PIM-7984: Add reference entity attribute option resources

Author: LaurentPetard

content/php-client/resources/reference-entity/attribute-options.md

@@ -0,0 +1,47 @@
+### Reference entity attribute option
+
+::: warning
+This resource is only available in the [Entreprise Edition](https://www.akeneo.com/enterprise-edition/).
+:::
+
+#### Get an attribute option for a given attribute of a given reference entity
+
+```php
+$client = new \Akeneo\PimEnterprise\ApiClient\AkeneoPimEnterpriseClientBuilder('http://akeneo.com/')->buildAuthenticatedByPassword('client_id', 'secret', 'admin', 'admin');
+
+/*
+ * Returns an array like this:
+ * [
+ *     'code'   => 'red',
+ *     'labels' => [
+ *         'en_US' => 'Red',
+ *         'fr_FR' => 'Rouge',
+ *     ]
+ * ]
+ */
+$referenceEntityAttributeOption = $client->getReferenceEntityAttributeOptionApi()->get('designer', 'favorite_color', 'red');
+```
+
+#### Get the list of attribute options of a given attribute for a given reference entity
+
+```php
+$client = new \Akeneo\PimEnterprise\ApiClient\AkeneoPimEnterpriseClientBuilder('http://akeneo.com/')->buildAuthenticatedByPassword('client_id', 'secret', 'admin', 'admin');
+
+$referenceEntityAttributeOptions = $client->getReferenceEntityAttributeOptionApi()->all('designer', 'favorite_color');
+```
+
+#### Upsert an attribute option for a given attribute of a given reference entity
+
+If the attribute option does not exist yet, this method creates it, otherwise it updates it.
+
+```php
+$client = new \Akeneo\PimEnterprise\ApiClient\AkeneoPimEnterpriseClientBuilder('http://akeneo.com/')->buildAuthenticatedByPassword('client_id', 'secret', 'admin', 'admin');
+
+$client->getReferenceEntityAttributeOptionApi()->upsert('designer', 'favorite_color', 'blue', [
+    'code' => 'blue',
+    'labels' => [
+        'en_US' => 'Blue',
+        'fr_FR' => 'Bleu',
+    ]
+]);
+```