allow setting permissions on unix sockets

Hello, It would be useful to allow setting permissions on unix sockets. There was a recommendation somewhere to run kestrel as same user as www server, but that is not always a good thing to do. For example my security model assumes there are many apps behind my reverse proxy and they do not need access to other apps, and the server also does not need access to directories and files of these apps, just to the socket. Of course one solution to the problem is containerization, but I don't think it is/should be the only solution. Plain user isolation also should work relatively straightforward.