[UI/UX:Developer] Black history month duck (#10169)

![Screen Shot 2024-02-08 at 1 52 51
AM](https://github.com/Submitty/Submitty/assets/123261952/d4d7f569-fda1-4720-9f73-0cbe4aecb136)

To embrace and welcome all community, we are adding black history month
duck.
The design is the three common theme color of  black history month. 
It will be visible randomly during entire february.

site/app/controllers/GlobalController.php

@@ -493,7 +493,6 @@ private function getDuckImage(\DateTime $now): string {
         switch ($month) {
             case 12:
                 //December (Christmas, Hanukkah)
-
                 $hanukkahStartDateTime = $this->calculateHanukkahDate($yearint);
                 $hanukkahEndDateTime = $this->calculateHanukkahDate($yearint);
                 $hanukkahEndDateTime->modify('+8 days');
@@ -556,13 +555,15 @@ private function getDuckImage(\DateTime $now): string {
                 }
                 break;
             case 2:
+                $februaryImages = ['moorthy_duck/black-history-duck.svg'];
                 if ($day <= 3) {
-                    $duck_img = 'moorthy_duck/party-duck/party-duck-10th.svg';
+                    $februaryImages[] = 'moorthy_duck/party-duck/party-duck-10th.svg';
                 }
                 //Valentines (Hearts)
                 if ($day >= 11 && $day <= 17) {
-                    $duck_img = 'moorthy_duck/02-february.svg';
+                    $februaryImages[] = 'moorthy_duck/02-february.svg';
                 }
+                $duck_img = $februaryImages[array_rand($februaryImages)];
                 break;
             case 1:
                 //January (Snowflakes)