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/defaults/main.yml

@@ -0,0 +1,23 @@
+grafana_ldap_enabled: false
+grafana_http_addr:
+grafana_ldap_host: 127.0.0.1
+grafana_ldap_port: 389
+grafana_ldap_ssl: false
+grafana_ldap_start_tls: false
+grafana_ldap_bind_dn: cn=admin,dc=grafana,dc=org
+grafana_ldap_bind_password: grafana
+grafana_ldap_search_filter: (cn=%s)
+grafana_ldap_search_base_dns:
+- dc=grafana,dc=org
+grafana_ldap_attr_name: givenName
+grafana_ldap_attr_surname: sn
+grafana_ldap_attr_username: cn
+grafana_ldap_attr_member_of: memberOf
+grafana_ldap_attr_email: email
+grafana_ldap_group_mappings:
+- group_dn: cn=admins,ou=groups,dc=grafana,dc=org
+  org_role: Admin
+- group_dn: cn=users,ou=groups,dc=grafana,dc=org
+  org_role: Editor
+- group_dn: '*'
+  org_role: Viewer