Add 5.0.5 release note page

docs/releases/5.0.5.md

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+# Wagtail 5.0.5 release notes
+
+_October 19, 2023_
+
+```{contents}
+---
+local:
+depth: 1
+---
+```
+
+## What's new
+
+### CVE-2023-45809: Disclosure of user names via admin bulk action views
+
+This release addresses an information disclosure vulnerability in the Wagtail admin interface. A user with a limited-permission editor account for the Wagtail admin can make a direct URL request to the admin view that handles bulk actions on user accounts. While authentication rules prevent the user from making any changes, the error message discloses the display names of user accounts, and by modifying URL parameters, the user can retrieve the display name for any user. The vulnerability is not exploitable by an ordinary site visitor without access to the Wagtail admin.
+
+Many thanks to quyenheu for reporting this issue. For further details, please see [the CVE-2023-45809 security advisory](https://github.com/wagtail/wagtail/security/advisories/GHSA-fc75-58r8-rm3h).