feat(laravel-api-problem): add method getInstance

Author: pedrosalpr

src/Http/LaravelHttpApiProblem.php

@@ -99,6 +99,11 @@ public function getStatusCode(): int
         return $this->statusCode;
     }
 
+    public function getInstance(): string
+    {
+        return $this->instance;
+    }
+
     public function getExtensions(): array
     {
         return $this->extensions;

src/LaravelApiProblemInterface.php

@@ -19,4 +19,6 @@ public function getDetail(): string;
     public function getExtensions(): array;
 
     public function getHeaderProblemJson(): string;
+
+    public function getInstance(): string;
 }