roles/grafana: Deploy Grafana

This commit introduces the *grafana* role and the corresponding
`grafana.yml` playbook.  The role installs Grafana using the system
package manager, and configures the server (including LDAP
authentication).

roles/grafana/files/grafana.nginx.conf

@@ -0,0 +1,3 @@
+location / {
+    proxy_pass http://[::1]:3000/;
+}