Ability to Quickly Switch Between Saved Custom Upstream DNSs

I use a smart DNS service for unblocking international content, but only sometimes, when I need it. Otherwise I use GoogleDNS. It would make things much easier if I were able to quickly switch between GoogleDNS and a saved custom DNS on the web interface.

Pihole's web interface offers the ability to select different/custom upstream DNS servers. They can be selected easily and changed as users want.