Request to add a flag to set unix domain socket permissions

[emilfihlman]

It would be really good if there was a flag, maybe -m / --mode that would allow us to set the permissions for the unix domain socket.
Otherwise the default umask doesn't allow most distribution default setting proxies from accessing the socket xandikos creates.

Ie usage could be for example xandikos --defaults -d /path/to/directory --listen /path/to/socket --mode 666

[jelmer]

Note that this is nontrivial since aiohttp/Python don't expose this:

https://docs.aiohttp.org/en/stable/_modules/aiohttp/web_runner.html#UnixSite

python/cpython#94984