[Route] Add route for DDM activations learn more page (#50465)

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**Related issue:** Resolves #48222

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## Summary by CodeRabbit

* **Documentation**
* Added a redirect from the DDM activations information page to the
relevant section of the Custom OS Settings article.
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Co-authored-by: Eric <eashaw@sailsjs.com>

website/config/routes.js

@@ -1379,6 +1379,7 @@ module.exports.routes = {
   'GET /learn-more-about/idp-account-sync': '/guides/deploying-apple-account-provisioning-with-fleet',
   'GET /learn-more-about/security-posture': 'https://developers.google.com/android/management/reference/rest/v1/enterprises.devices#DevicePosture',
   'GET /learn-more-about/software-update-status': 'https://developers.google.com/android/management/reference/rest/v1/enterprises.devices#SystemUpdateInfo',
+  'GET /learn-more-about/ddm-activations': '/guides/custom-os-settings#apple-declarations-ddm',
   'GET /learn-more-about/linux-disk-encryption': '/guides/enforce-disk-encryption#enforce-disk-encryption-on-linux',
   'GET /learn-more-about/removal-behavior': '/guides/custom-os-settings#removal-behavior',
   'GET /learn-more-about/android-manual-sync': '/guides/how-to-manually-sync-an-android-device',