Redirect hydra and nixops manuals to the latest hydra builds

[samueldr]

With the move to netlify, the hydra and nixops manuals vanished, without a redirect. Considering search engines link to those manuals, I believe it's mandatory we keep cool URIs working.

Use a "200" redirect.

200: "OK". Redirects with this status code will change the server response without changing the URL in the browser address bar. This is used for rewrites and proxying.

• https://docs.netlify.com/routing/redirects/redirect-options/#http-status-codes

This will keep the nixos.org/.../manual URL in the address bar, but serve the contents proxied from the hydra result.

[edolstra]

These should be regular redirects, to proxies, since these pages are not part of the NixOS website and don't have the same styling.

[edolstra]

I've changed them to 302.