I just checked again, and contrary to their announcements, Drone 1.0.0 is still RC and the install instructions aren't great yet. But in order to build ourselves, I think we first need to set up a Kosmos Drone CI that all repos/users on this Gitea can use.
Asked on the forums: https://discourse.gitea.io/t/how-to-turn-off-email-notifications/829
Turns out everything already works perfectly. A simple ark backup create [name] will create a complete backup of all our resources and upload the files to the storage bucket. It will also create volume snapshots, which are a native feature of GCP, and which you can find here.
I started setting up Ark, as it looks like the best open-source solution to me. Went through https://heptio.github.io/ark/v0.10.0/gcp-config and have an ark deployment running on the sidamo cluster now.