Add duplicate() function to Query Builder

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

src/Functions/Duplicate.php

@@ -0,0 +1,35 @@
+<?php
+
+namespace Arendsen\FluxQueryBuilder\Functions;
+
+use Arendsen\FluxQueryBuilder\Type;
+use Arendsen\FluxQueryBuilder\Type\ArrayType;
+
+class Duplicate extends Base
+{
+    /**
+     * @var string $column
+     */
+    private $column;
+
+    /**
+     * @var string $as
+     */
+    private $as;
+
+    public function __construct(string $column, string $as)
+    {
+        $this->column = $column;
+        $this->as = $as;
+    }
+
+    public function __toString()
+    {
+        $input = new ArrayType([
+            'column' => $this->column,
+            'as' => $this->as
+        ]);
+
+        return '|> duplicate(' . $input . ') ';
+    }
+}