hydra: bayfront: Have NGinx serve reproducible.json from QA.

This file is written and updated by the qa-frontpage, and is consumed
by https://ismypackagereproducibleyet.org/

* hydra/bayfront.scm (%qa.guix.gnu.org-nginx-servers): Serve
reproducible.json.

hydra/bayfront.scm

@@ -763,7 +763,13 @@ proxy_set_header  Via  $via;"
        (uri "/")
        (body '("proxy_pass http://qa-frontpage;"
                "proxy_http_version 1.1;"
-               "proxy_set_header Connection \"\";"))))))))
+               "proxy_set_header Connection \"\";")))
+      (nginx-location-configuration
+       (uri "/reproducible.json")
+       (body '("alias /var/lib/qa-frontpage/reproducible.json;"
+               "add_header Content-Type 'text/plain; charset=UTF-8';"
+               "gzip_static always;"
+               "gunzip on;"))))))))
 
 (define %packages.guix.gnu.org-nginx-servers
   (list