configure am/pm time-format as user preference (#2789)

src/Utils/DateFormatConverter.php

@@ -0,0 +1,33 @@
+<?php
+
+/*
+ * This file is part of the Kimai time-tracking app.
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace App\Utils;
+
+class DateFormatConverter
+{
+    /**
+     * This defines the mapping between PHP date format (key) and ICU date format (value).
+     * https://unicode-org.github.io/icu/userguide/format_parse/datetime/#datetime-format-syntax
+     *
+     * @var array
+     */
+    private static $formatConvertRules = [
+        // hours
+        'h' => 'hh', 'H' => 'HH',
+        // minutes
+        'i' => 'mm',
+        // am/pm to AM/PM
+        'A' => 'a'
+    ];
+
+    public function convert(string $format): string
+    {
+        return strtr($format, self::$formatConvertRules);
+    }
+}