Introduce OpenBSD platform icon (#3713)

When the platform is OpenBSD, add an appropriate "platform" png in the
public directory for use.

<img width="329" height="66" alt="image"
src="https://github.com/user-attachments/assets/2145c95b-a8c7-4768-bb03-6e9a15443248"
/>

Image taken from:
https://www.streamlinehq.com/icons/download/openbsd--31088


Closes: #3710

Author: josephsnyder

app/cdash/app/Controller/Api/Index.php

@@ -674,6 +674,8 @@ public function generateBuildResponseFromRow(array $build_array): array|false
             $buildplatform = 'linux';
         } elseif (strtolower(substr($build_array['osname'], 0, 7)) === 'freebsd') {
             $buildplatform = 'freebsd';
+        } elseif (strtolower(substr($build_array['osname'], 0, 7)) === 'openbsd') {
+            $buildplatform = 'openbsd';
         } elseif (strtolower(substr($build_array['osname'], 0, 3)) === 'gnu') {
             $buildplatform = 'gnu';
         }