Sign-out deletes only GitLab site data, not all subdomains

What does this MR do and why?

Sign-out deletes only GitLab site data, not all subdomains

Fix sign out process to not delete cookies from all 'sibling' sub-domains through loop-deletting available cookies instead of using Clear-Site-Data header that seems to delete cookies from the entire domain.

Originally from community contribution MR !142740

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Before	After

How to set up and validate locally

1. Ensure your local GDK is using NGinx and a hostname
2. Change your hostname to a subdomain like subdomain.gdk.test . We will also need a second subdomain like othersubdomain.gdk.test ; make sure these are both present in /etc/hosts
3. gdk reconfigure and gdk restart to use the subdomain for your hostname
4. Set up othersubdomain in Nginx: add the following block to gitlab-development-kit/nginx/conf/nginx.conf after the last server {} block in the file:

   server {
    listen othersubdomain.gdk.test:3444;
   
    location / {
      add_header Set-Cookie "tst_cook=capybara; Domain=othersubdomain.gdk.test" always;
   
      root ../gitlab/public/;
      index 422.html;
    }
   }

5. (optional) gdk doctor - ensure this does not output the message nginx/conf/nginx.conf is not valid!
6. gdk restart nginx
7. Visit http://othersubdomain.gdk.test:3444 in your browser.
   • You should see the 422 error page.
   • Check the cookies for this page in your browser's Web Inspector. You should see the tst_cook cookie with "Domain" listed as othersubdomain.gdk.test
8. Visit GitLab in your browser at https://subdomain.gdk.test:3443 (or whatever subdomain and port you have chosen)
9. Log in, if needed
10. Log out
11. Reload the web inspector for the page othersubdomain.gdk.test - the cookie for that subdomain should still be present