Merge branch 'dast-update-authentication-docs' into 'master'

Update DAST Authentication page to reflect correct limitations

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/149512



Merged-by: Russell Dickenson <rdickenson@gitlab.com>
Approved-by: Cameron Swords <cswords@gitlab.com>
Approved-by: Russell Dickenson <rdickenson@gitlab.com>
Co-authored-by: Arpit Gogia <12347103-arpitgogia@users.noreply.gitlab.com>