Support using Redis with UDS

[niklasmohrin]

Redis has the option to connect via unix domain sockets. I have such a setup running with

services.redis."r1" = {
    enable = true;
    port = 0; # disable listening via TCP
    extraConfig = ''
      locale-collate "C"
      unixsocket ../redis.socket
      unixsocketperm 777
    '';
  };
};
settings.processes."r1".readiness_probe.exec.command = lib.mkForce "true";

The ../redis.socket places the socket in the data directory instead of next to the dump.rdb file. The locale-collate setting should be unneeded for this, but I haven't checked if it is relevant for UDS.

The change in the readiness probe is needed because the current command, ${config.package}/bin/redis-cli -p ${toString config.port} ping relies on TCP being active. If setup properly, this should probably perform the same ping, but through the socket.

It would be nice if there would be an option like uds = "data/redis.socket" to take care of all of this. Please let me know what you think :)

[shivaraj-bh]

Could you check if #353 works for you?