r/grafana: Fix Origin not allowed error

Grafana 8.3.5 introduced a new CSRF protection mechanism that requires
the value of the Host HTTP request header to be preserved from the
original client request.

https://github.com/grafana/grafana/issues/45117#issuecomment-1033842787

roles/grafana/files/grafana.nginx.conf

@@ -1,3 +1,4 @@
 location / {
     proxy_pass http://[::1]:3000/;
+    proxy_set_header Host $http_host;
 }