add url to page

- url is now retreived in the endpoint "->pages()->find($pageId)"
- url can now be read by the user in a straightforward way

[added to notion-api at 2021-07-02]
[https://developers.notion.com/changelog/page-objects-now-return-url]

Author: johguentner

src/Entities/Page.php

@@ -31,6 +31,11 @@ class Page extends Entity
      */
     protected string $title = '';
 
+    /**
+     * @var string
+     */
+    protected string $url = '';
+
     /**
      * @var string
      */
@@ -101,6 +106,7 @@ private function fillFromRaw(): void
         $this->fillObjectType();
         $this->fillProperties();
         $this->fillTitle(); // This has to be called after fillProperties(), since title is provided by properties
+        $this->fillUrl();
         $this->fillCreatedTime();
         $this->fillLastEditedTime();
     }
@@ -151,6 +157,16 @@ private function fillTitle(): void
         }
     }
 
+    /**
+     * 
+     */
+    private function fillUrl(): void
+    {
+        if (Arr::exists($this->responseData, 'url')) {
+            $this->url = $this->responseData['url'];
+        }
+    }
+
     /**
      * @param $propertyTitle
      * @param $property
@@ -324,6 +340,14 @@ public function getTitle(): string
         return $this->title;
     }
 
+    /**
+     * @return string
+     */
+    public function getUrl(): string
+    {
+        return $this->url;
+    }
+
     /**
      * @return Collection
      */