Rename Public access to Project visibility

While reviewing: gitlab!65671 (merged), it occurred that we should rename the page.

This MR is to match the title of the topic with the navigation item.

• Before: https://docs.gitlab.com/ee/public_access/public_access.html
• After: http://eread-rename-public-access-nav-item.178.62.207.141.nip.io/ee/public_access/public_access.html

CC @sselhorn