Add Terms of Service/Privacy Policy and Email consent for Sourcegraph Server

Created by: limitedmage

RFC here: https://docs.google.com/document/d/1EK-bm5USxvC7WVGcHvFRl0bQfqE3dcyFQtHsVWPkEeE/edit

• #28717
• #28950
• #29020