nixos/jack,pulseaudio: fix pulse connection to jackd service

This fixes the case when Jack Audio Daemon is running
as a service via `services.jack.jackd` and Pulseaudio
running as a *user* service.

Two issues prevented connecting `pulse` with `jackd`:
* Missing `JACK_PROMISCUOUS_SERVER` environment variable for `pulse` user service,
  resulting in `pulse` trying to access `jackd` as if it was running as part of
  the users session.
* `jackd` not being able to access socket created by `pulse` due to socket
  created using user ID and `users` group. Change allows `jackd` to access
  the socket created by `pulse` correctly.

`pulse` now also autoloads `module-jack-sink` and `module-jack-source`
if `services.jack.jackd.enable` is set.

The default `pulse` package is now set to `pulseaudioFull` automatically
if `services.jack.jackd.enable` is set.

nixos/modules/services/audio/jack.nix

@@ -246,6 +246,9 @@ in {
         description = "JACK Audio Connection Kit";
         serviceConfig = {
           User = "jackaudio";
+          SupplementaryGroups = lib.optional
+            (config.hardware.pulseaudio.enable
+            && !config.hardware.pulseaudio.systemWide) "users";
           ExecStart = "${cfg.jackd.package}/bin/jackd ${lib.escapeShellArgs cfg.jackd.extraOptions}";
           LimitRTPRIO = 99;
           LimitMEMLOCK = "infinity";