feat: add unix socket listener

[zachsmith1]

• this PR enables an optional mode for binding to a unix-socket instead of the default host/port listener
• this allows us to decouple the iroh-gateway container from the envoy pod deployment
• previously, if we wanted to bump the iroh-gateway version it would be rolling out the envoy pod since the iroh-gateway container runs inside it. this new model will allow us to run iroh-gateway as a daemonset next to envoy daemonset and then share the nodes unix socket. the other option would be to use a svc with locality but that adds overhead and an extra network hop (kube-proxy/IPVS/iptables and TCP stack).
• UDS model is low overhead and strictly node-local

[zachsmith1]

Putting this in wip until we split out some things due to windows build complaining due to shared libs

[Frando]

I can just add UDS support to iroh-proxy-utils, it'll save you the additional TCP connection.

[Frando]

I added UnixListener support to iroh-proxy-utils: n0-computer/iroh-proxy-utils#10
Will merge and post a PR to update the app to latest iroh-proxy-utils, then you can adapt this PR to use DownstreamProxy::forward_uds_listener and skip the additional TCP connection.

#66 contains the bump to latest iroh-proxy-utils - feel free to merge that and then update your PR here afterwards.