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/defaults/main.yml

@@ -1,3 +1,4 @@
+grafana_domain: '{{ ansible_fqdn }}'
 grafana_ldap_enabled: false
 grafana_http_addr:
 grafana_ldap_host: 127.0.0.1

roles/grafana/files/grafana.nginx.conf

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

roles/grafana/templates/grafana.ini.j2

@@ -38,7 +38,7 @@ http_addr = {{ grafana_http_addr }}
 http_port = 3000
 
 # The public facing domain name used to access grafana from a browser
-domain = localhost
+domain = {{ grafana_domain }}
 
 # Redirect to correct domain if host header does not match domain
 # Prevents DNS rebinding attacks