[Enhancement] Allow to set custom dns servers

[GoudronViande24]

I have a pihole on my network and would like to be able to use it for the DNS server. It could also be used by others to use custom servers

[clientenq]

If you use this script on the device running pihole service, you can select the current dns option when it asks which dns you like to use for your openvpn setup. Your device(s) connecting via the generated openvpn configuration will then use the pihole dns service (if pihole is configured correctly).

This script for the openvpn service does not affect the configuration of your pihole service. Please contact the pihole community if you have issues how to configure pihole.

[GoudronViande24]

I was installing this on another device than the pi-hole and that doesn't have the pi-hole DNS. I have to manually edit them after in the openvpn config file. This issue is more a possible enhancement than an actual issue.

Many of the other openvpn scripts have this option so that's why

(sorry for the bad english)

[CagdasOZGUR]

Can a dns server be selected each time a new client is added?
Just like with WireGuard you did. Pleaseee.