add new linux package "zrok-agent"

[qrkourier]

run the agent as a system service

there's no need to rebase the account env because this will be a new package, and the account env will always be created and managed by the new package

include a user service, i.e., systemctl --user enable --now zrok-agent.service, too; there's no need for a user service template like [email protected] because no one needs multiple agents per zrok account env

[michaelquigley]

I would avoid any sort of automation around rebasing. This really should be something that a user initiates knowingly.

[qrkourier]

Correct. The agent package will not rebase in any scenario because it's introduced with v1, so there's no potential problem until v2.