added first and last fields for invoices (#3594)

tests/Invoice/Renderer/DebugRendererTest.php

@@ -72,6 +72,8 @@ class DebugRendererTest extends TestCase
         self::assertEquals($begin->format('m'), $data['model']['query.month_number']);
         self::assertEquals($begin->format('d'), $data['model']['query.day']);
         // TODO check values or formats?
+        self::assertEquals('2020.08.12', $data['model']['invoice.first']);
+        self::assertEquals('2022.10.23', $data['model']['invoice.last']);
     }
 
     protected function assertModelStructure(array $model, int $projectCounter = 0, int $activityCounter = 0)
@@ -89,6 +91,8 @@ class DebugRendererTest extends TestCase
             'invoice.tax_plain',
             'invoice.total_time',
             'invoice.duration_decimal',
+            'invoice.first',
+            'invoice.last',
             'invoice.total',
             'invoice.total_nc',
             'invoice.total_plain',