Allow connections to self

[dpc]

I remember watching one of the Iroh introduction binaries when it was said that Endpoints can not connect to self, because it can lead to bad things in distributed systems.

I can very much understand the premise, as it's easy to get into sort of endless echos etc. situation, but ... in a lot of cases being able to e.g. uniformly query "self" just like any other peer is very useful and simplifies code and the system a lot. Would be neat if it was possible to opt-in into ability to call self, if technically under the hood Iroh stack could handle it.