Add a systemd user service to start the ssh-agent and add an ssh
config to automatically add ssh identities to the agent when they
are used (otherwise we have to add them manually). I will see how
this works out.
See: https://wiki.archlinux.org/title/SSH_keys#SSH_agents
dotdrop wants to use a profile for each system it is deployed. We
want to use some common settings on all hosts without having to c-
reate a profile for each.