[New Docs]: Add docs feature picker

[timdeschryver]

Information

We need a version picker so users can look at the old version(s) of our docs.
This can be similar as the selector to our current docs, if you have a better idea feel free to suggest one in the comments before picking this up.

Documentation page

https://deploy-preview-4959--ngrx-site-v19.netlify.app

I would be willing to submit a PR to fix this issue

• Yes
• No