grafana: enable HTTP/2 in nginx

roles/grafana/templates/nginx.conf.j2

@@ -32,9 +32,9 @@ server {
 {% if grafana_ssl_enabled is defined and
       grafana_ssl_enabled %}
 server {
-    listen 443 ssl;
+    listen 443 ssl http2;
 {% if ansible_all_ipv6_addresses | length %}
-    listen [::]:443 ssl;
+    listen [::]:443 ssl http2;
 {% endif %}
     server_name {{ grafana_domain }};
 
@@ -51,6 +51,8 @@ server {
     ssl_dhparam {{ grafana_ssl_dhparam }};
 {% endif %}
 
+    proxy_set_header Host $http_host;
+
     location /login {
         limit_req zone=req_grafana_login burst=10;
         proxy_pass http://grafana_backend;