Before this change it wasn't possible to see where transfers were
going from and to in core/stats and core/transferred.
When use in rclone mount in particular this made interpreting the
stats very hard.
- add support for unix sockets (which skip the auth).
- add support for multiple listeners
- collapse unnecessary internal structure of lib/http so it can all be
imported together
- moves files in sub directories of lib/http into the main lib/http
directory and reworks the code that uses them.
See: https://forum.rclone.org/t/wip-rc-rcd-over-unix-socket/33619Fixes: #6605