Check validators are online

[onmax]

To improve the reliability of the API, we could check if the addresses submitted in the /public/validators files are real online validators.

If they appear to be offline, then move the files to a folder called offline.

This is just an idea, but we should think about how to handle this case.

[Albermonte]

I think we are only tracking online validators already, so if it is not active it won't be returned in the endpoint. We would have to create the offline part only