minor #1794 [Site] adjust external link config (kbond)

This PR was merged into the 2.x branch.

Discussion
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[Site] adjust external link config

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| Issues        | n/a
| License       | MIT

Don't mark any `*symfony.com` link as _external_.

Commits
-------

6a8995a [Site] adjust external link config

Author: kbond

ux.symfony.com/src/Service/CommonMark/ConverterFactory.php

@@ -38,6 +38,9 @@ public function __invoke(): CommonMarkConverter
                     'generator' => 'https://github.com/symfony/ux/issues/%d',
                 ],
             ],
+            'external_link' => [
+                'internal_hosts' => ['/(^|\.)symfony\.com$/'],
+            ],
         ]);
 
         $converter->getEnvironment()