How do you add key chain to menu bar in 10.13.2

That doesn't exist anymore. Apple added a Lock Screen item in the Apple menu, but I know it doesn't offer all the functionality that the Keychain menu had.

There are a few other posts on this. They may have some info on workarounds to get the functionality you want.

That option has been removed in High Sierra.

You can register your feedback—Apple Feedback http://www.apple.com/feedback/

As an Alternative you can drag the app to the Dock or the Finder tool bar by holding the command key.

The lock screen and Keychain in the menu bar seem to be completely different things

I understand that. That's why I mentioned it when I noted the changes made by Apple.