Add aggregateWindow() function to Query Builder

Signed-off-by: davidarendsen <davidarendsen@hey.com>

tests/Functions/AggregateWindowTest.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Tests\Functions;
+
+use Arendsen\FluxQueryBuilder\Functions\AggregateWindow;
+use PHPUnit\Framework\TestCase;
+
+final class AggregateWindowFunctionTest extends TestCase
+{
+    public function testSimpleWindow()
+    {
+        $expression = new AggregateWindow('20s', null, null, 'mean');
+
+        $query = '|> aggregateWindow(every: 20s, fn: mean) ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+
+    public function testAllParameters()
+    {
+        $expression = new AggregateWindow('20s', 'every', '0s', 'mean', 'location', '_value', '_stop', '_time', false);
+
+        $query = '|> aggregateWindow(every: 20s, period: every, offset: 0s, fn: mean, location: "location", ' .
+            'column: "_value", timeSrc: "_stop", timeDst: "_time", createEmpty: false) ';
+
+        $this->assertEquals($query, $expression->__toString());
+    }
+}