NGINX improvements

What does this Merge Request do?

This MR:

• Updates NGINX settings docs.
• Prints a => http://gdk.test:3000/ should be ready shortly. message when starting/restarting.
• Makes config.__uri smarter by not producing http://gdk.test:80 or https://gdk.test:443 URLs.
• Adds spec coverage for config.__uri

Merge Request checklist

• Tests added for new functionality. If not, please raise Issue to follow-up.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Documentation added/updated, if needed.
• gdk doctor test added, if needed.