Custom filter on specific properties using ApiFilter annotation

When using `ApiFilter` annotation, it seems that you have to set the concerned properties in the annotation itself.

Author: vvatelot

core/filters.md

@@ -951,6 +951,27 @@ class Offer
 }
 ```
 
+When using `ApiFilter` annotation, you can specify specific properties for which the filter will be applied:
+```
+<?php
+// api/src/Entity/Offer.php
+
+namespace App\Entity;
+
+use ApiPlatform\Core\Annotation\ApiFilter;
+use ApiPlatform\Core\Annotation\ApiResource;
+use App\Filter\RegexpFilter;
+
+/**
+ * @ApiResource
+ * @ApiFilter(RegexpFilter::class, properties={"email","anOtherProperty"})
+ */
+class Offer
+{
+    // ...
+}
+```
+
 You can now enable this filter using URLs like `http://example.com/offers?regexp_email=^[FOO]`. This new filter will also
 appear in Swagger and Hydra documentations.