A swarm's services and its hives can live on different hosts, and a host
has no way to tell whether it is the one holding the root — so setting
the swarm CA up is an operator action, not something a host infers.
`swarm.ca.autoConfigure` is off by default and is the only thing that
issues a hive sub-CA, which is also the only case that *can*: signing
one needs the root's private key, and that key is deliberately not on a
hive host otherwise.
With the flag off, a hive self-signs its CA exactly as it always has.
That keeps a plain hive working out of the box; what it gives up is
membership of a swarm's trust hierarchy, which is the right thing to
give up for a hive nobody has federated.
Replaces a default derived from `swarm.peers == { }`. That read "no
peers declared" as "everything is local", which is not the same claim —
a hive can belong to a swarm it has not declared yet, or to one whose
services run elsewhere entirely.
cc74a2c1f6