Note the deprecation of admin_vulnerability permission

What does this MR do and why?

Note the deprecation of admin_vulnerability being removed from Developers

In GitLab 16.4 we deprecated the admin_vulnerability permission for Developers. This MR updates our documentation with the deprecation entry.

• Update the permissions table at https://docs.gitlab.com/ee/user/permissions.html
• Add mention of the new custom role in https://docs.gitlab.com/ee/user/permissions.html#custom-roles. Already included, please review.
• Add mention of a role, or custom role, as a prerequisite in https://docs.gitlab.com/ee/user/application_security/vulnerabilities/#change-status-of-a-vulnerability
  • That developer, maintainer, or owner role is required to change a vulnerability's status should have already been documented.

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