the current version of woodpecker-server in stable now has the features this was original used for, not other usages of unstable are in tree left so removing it.
With the shared system token, every time the Woodpecker host would
restart, a new Woodpecker agent registration would be created, because
the agent receives a unique ID on first connection using the system
token, which it couldn't store however, because it doesn't have a
writable config file in NixOS.
Use an agent token now, which doesn't require the agent to store a
unique ID in a wrtiable config, therefore not making it re-register.
Also see:
https://woodpecker-ci.org/docs/administration/agent-config#agent-registration
