Add category object and category_id to document resource

The endpoint api/documents don't return the category of invoice/bill as
the endpoint api/transactions do. With this change will be possible
return this value.

Signed-off-by: Vitor Mattos <vitor@php.rio>

app/Http/Resources/Document/Document.php

@@ -8,6 +8,7 @@
 use App\Http\Resources\Document\DocumentItem;
 use App\Http\Resources\Document\DocumentItemTax;
 use App\Http\Resources\Document\DocumentTotal;
+use App\Http\Resources\Setting\Category;
 use App\Http\Resources\Setting\Currency;
 use Illuminate\Http\Resources\Json\JsonResource;
 
@@ -32,6 +33,8 @@ public function toArray($request)
             'due_at' => $this->due_at ? $this->due_at->toIso8601String() : '',
             'amount' => $this->amount,
             'amount_formatted' => money($this->amount, $this->currency_code, true)->format(),
+            'category_id' => $this->category_id,
+            'category' => new Category($this->category),
             'currency_code' => $this->currency_code,
             'currency_rate' => $this->currency_rate,
             'contact_id' => $this->contact_id,