Add banner linking to new docs on old documentation site

[daniela-bonvini]

Describe the problem that you experienced

Nowhere in the old documentation is cited the new docs site

Enter the URL of the topic with the problem

https://angular.io/

Describe what you were looking for in the documentation

No response

Describe the actions that led you to experience the problem

When searching for "Angular docs" on a search engine (I tried with Google, Firefox and Edge), the first result is very likely to be angular.io instead of the newer angular.dev

Describe what you want to experience that would fix the problem

Since there is the new angular.dev documentation and the old one is going to be deprecated in the near future, I suggest implementing at the top of the old doc site a banner saying that there is a newer site to reference, with a link to it

Add a screenshot if that helps illustrate the problem

No response

If this problem caused an exception or error, please paste it here

No response

If the problem is browser-specific, please specify the device, OS, browser, and version

No response

Provide any additional information here in as much as detail as you can

No response

[JeanMeche]

Currently Angular.dev isn't indexed as it's still in a beta status (cf https://angular.dev/robots.txt)

[twerske]

We will be adding a redirect in v18 for people to automatically be brought to Angular.dev starting the next release!

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