Well, provided “grafanadashboard” resolves in DNS (or a local hosts file) to
the IP address of your Grafana server, all you need to do is get Grafana to
listen on port 80 instead of 3000.
http_port setting in the [server] section of /etc/grafana/grafana.ini
Of course, make sure nothing else (eg: Apache, Nginx) is trying to use port 80
on the same machine.
I guess you need some more to do to get the right dashboard displayed. Take a web server (Apache, nginx, …) as reverse proxy and call the destination dashboard referring to the called url.
Regards
Andre