website: Tell search engines not to index numbered pages.

This change avoids polluting search results with pages that list
items, such as posts and packages, and gives more visibility to detail
pages instead (post and package detail pages).

* website/apps/blog/templates/post-list.scm (post-list-t): Don't index.
* website/apps/blog/templates/tag.scm (tag-t): Likewise.
* website/apps/packages/templates/package-list.scm (package-list-t): Likewise.

Signed-off-by: Mathieu Othacehe <othacehe@gnu.org>

website/apps/blog/templates/post-list.scm

@@ -30,6 +30,7 @@
 system|GNU Hurd|GNU Guix package manager|GNU Guile|Guile \
 Scheme|Transactional upgrades|Functional package \
 management|Reproducibility") #\|)
+     #:index? #false
      #:active-menu-item (C_ "website menu" "Blog")
      #:css
      (list (guix-url "static/base/css/page.css")

website/apps/blog/templates/tag.scm

@@ -34,6 +34,7 @@
 system|GNU Hurd|GNU Guix package manager|GNU Guile|Guile \
 Scheme|Transactional upgrades|Functional package \
 management|Reproducibility") #\|)
+     #:index? #false
      #:active-menu-item (C_ "website menu" "Blog")
      #:css
      (list (guix-url "static/base/css/page.css")

website/apps/packages/templates/package-list.scm

@@ -31,6 +31,7 @@
 system|GNU Hurd|GNU Guix package manager|GNU Guile|Guile \
 Scheme|Transactional upgrades|Functional package \
 management|Reproducibility") #\|)
+     #:index? #false
      #:active-menu-item (C_ "website menu" "Packages")
      #:css
      (list (guix-url "static/base/css/page.css")