Is your feature request related to a problem? Please describe.
I wouldn't call it a problem, but there is no _up metric exported.

Describe the solution you'd like
I would like to have _up metric exported so it's easier to write an alert that NGINX is down.

Describe alternatives you've considered
None yet.

Additional context
Maybe there is another way to write the above alert with the data that's already exported but I am not aware of it yet.

Thank you.