Rename Webhooks to Filtering outbound requests

Update navigation item in global navigation

This merge request renames the Webhooks nav item, nested under Administer > Secure your installation, to Filtering outbound requests.

This is because that section was retitled in gitlab!113643 (merged).

• Link to the merge request that introduced the new page changed an existing page title: gitlab!113643 (merged)
• Give the MR a descriptive title.
• Optional. Link to the review app showing the new page: https://ld-main-patch-03014.docs.gitlab-review.app/ee/security/