Add noindex option

[JoeBerkley]

While we do have the ability to disallow crawling with the Robots.txt feature, we might still want crawling, but for search engines to not yet index the site.

Here's a good explanation on how this works from Google's webmaster support pages
https://support.google.com/webmasters/answer/93710?hl=en

[jagbarcelo]

I was just commenting the lack of noindex functionality in OrchardCore and how could it be implemented here. I think this module would be the perfect place for this exact feature.