Merge branch 'bugfix/6047_Add-missing-http2-to-nginx-config-proxy-protocol' into 'develop'

Add missing http2 directive to HTTPS proxy protocol config in nginx vhost conf

Closes #6047

See merge request ispconfig/ispconfig3!1406

Author: Marius Burkard

server/conf/nginx_vhost.conf.master

@@ -15,7 +15,7 @@ server {
         listen <tmpl_var name='ip_address'>:<tmpl_var name='https_port'> ssl http2;
 <tmpl_if name='use_proxy_protocol' op='==' value='y'>
 <tmpl_if name='proxy_protocol_https' op='>' value='0'>
-        listen <tmpl_var name='ip_address'>:<tmpl_var name='proxy_protocol_https'> ssl proxy_protocol;
+        listen <tmpl_var name='ip_address'>:<tmpl_var name='proxy_protocol_https'> ssl http2 proxy_protocol;
 </tmpl_if>
 </tmpl_if>