Update Signup URL

[russjones]

Purpose

To better support HA configurations instead of trying to find out which proxy the user should connect to, print <proxyhost> and tell the user to make sure the proxy is accessible.

Implementation

• Changed the signup message.

Related Issues

Fixes #1643

[klizhentas]

this seems backwards, I think we should add proper public addr there instead of replacing it back with placeholder

[kontsevoy]

@klizhentas we've discussed this internally, this is supposed to be a host name, not an IP address, for which we do not have a config. setting for (and adding one for printing these URLs) would be silly. Simply stating that makes it perfectly clear to admins what needs to be done.