set noindex on all content outside of https://istio.io/

[craigbox]

Google is confused about our duplicate content. We think it's all in the search index in order to power the custom search engine, but it looks like at least some that content is still available even though I've delisted it from the main search index.

That, and the facets don't actually correctly list versioned content.

My suggestion at this point is that we break site search for old versions, and then we add everything back, with a new engine if needed.

So, the first thing to do is to add noindex to the meta tags of every page on preliminary and archive.

https://developers.google.com/search/docs/crawling-indexing/block-indexing

Please do this in order:

(a) preliminary.istio.io (b) await validation (c) archive