installer: Add 'nss-certs' to the networking services.

Fixes <https://bugs.gnu.org/35469>.
Reported by Florian Pelz <pelzflorian@pelzflorian.de>.

* gnu/installer/services.scm (%system-services): Add service for
'nss-certs', with 'recommended?' set to #t.

gnu/installer/services.scm

@@ -89,6 +89,11 @@
       (name (G_ "Tor anonymous network router"))
       (type 'networking)
       (snippet '((service tor-service-type))))
+     (system-service
+      (name (G_ "Mozilla NSS certificates, for HTTPS access"))
+      (type 'networking)
+      (packages '((specification->package "nss-certs")))
+      (recommended? #t))
 
      ;; Network connectivity management.
      (system-service