kea: use separate runtime directories for each service

Kea may clean the runtime directory when starting (or maybe systemd does
it). I ran into this issue when restarting Kea after changing its
configuration, so I think the fact it normally doesn't clean it is a
race condition (it's cleaned on service start, and normally all Kea
services start at roughly the same time).

nixos/doc/manual/release-notes/rl-2311.section.md

···
 
 - `ssm-agent` package and module were renamed to `amazon-ssm-agent` to be consistent with the upstream package name.
 
+- `services.kea.{ctrl-agent,dhcp-ddns,dhcp,dhcp6}` now use separate runtime directories instead of `/run/kea` to work around the runtime directory being cleared on service start.
+
 ## Other Notable Changes {#sec-release-23.11-notable-changes}
 
 - The Cinnamon module now enables XDG desktop integration by default. If you are experiencing collisions related to xdg-desktop-portal-gtk you can safely remove `xdg.portal.extraPortals = [ pkgs.xdg-desktop-portal-gtk ];` from your NixOS configuration.

nixos/modules/services/monitoring/prometheus/exporters/kea.nix

···
       type = types.listOf types.str;
       example = literalExpression ''
         [
-          "/run/kea/kea-dhcp4.socket"
-          "/run/kea/kea-dhcp6.socket"
+          "/run/kea-dhcp4/kea-dhcp4.socket"
+          "/run/kea-dhcp6/kea-dhcp6.socket"
         ]
       '';
       description = lib.mdDoc ''

nixos/modules/services/networking/kea.nix

···
       DynamicUser = true;
       User = "kea";
       ConfigurationDirectory = "kea";
-      RuntimeDirectory = "kea";
       StateDirectory = "kea";
       UMask = "0077";
     };
···
       ];
 
       environment = {
-        KEA_PIDFILE_DIR = "/run/kea";
-        KEA_LOCKFILE_DIR = "/run/kea";
+        KEA_PIDFILE_DIR = "/run/kea-ctrl-agent";
+        KEA_LOCKFILE_DIR = "/run/kea-ctrl-agent";
       };
 
       restartTriggers = [
···
         ExecStart = "${package}/bin/kea-ctrl-agent -c /etc/kea/ctrl-agent.conf ${lib.escapeShellArgs cfg.ctrl-agent.extraArgs}";
         KillMode = "process";
         Restart = "on-failure";
+        RuntimeDirectory = "kea-ctrl-agent";
       } // commonServiceConfig;
     };
   })
···
       ];
 
       environment = {
-        KEA_PIDFILE_DIR = "/run/kea";
-        KEA_LOCKFILE_DIR = "/run/kea";
+        KEA_PIDFILE_DIR = "/run/kea-dhcp4";
+        KEA_LOCKFILE_DIR = "/run/kea-dhcp4";
       };
 
       restartTriggers = [
···
           "CAP_NET_BIND_SERVICE"
           "CAP_NET_RAW"
         ];
+        RuntimeDirectory = "kea-dhcp4";
       } // commonServiceConfig;
     };
   })
···
       ];
 
       environment = {
-        KEA_PIDFILE_DIR = "/run/kea";
-        KEA_LOCKFILE_DIR = "/run/kea";
+        KEA_PIDFILE_DIR = "/run/kea-dhcp6";
+        KEA_LOCKFILE_DIR = "/run/kea-dhcp6";
       };
 
       restartTriggers = [
···
         CapabilityBoundingSet = [
           "CAP_NET_BIND_SERVICE"
         ];
+        RuntimeDirectory = "kea-dhcp6";
       } // commonServiceConfig;
     };
   })
···
       ];
 
       environment = {
-        KEA_PIDFILE_DIR = "/run/kea";
-        KEA_LOCKFILE_DIR = "/run/kea";
+        KEA_PIDFILE_DIR = "/run/kea-dhcp-ddns";
+        KEA_LOCKFILE_DIR = "/run/kea-dhcp-ddns";
       };
 
       restartTriggers = [
···
         CapabilityBoundingSet = [
           "CAP_NET_BIND_SERVICE"
         ];
+        RuntimeDirectory = "kea-dhcp-ddns";
       } // commonServiceConfig;
     };
   })

nixos/tests/prometheus-exporters.nix

···
     };
 
     kea = let
-      controlSocketPathV4 = "/run/kea/dhcp4.sock";
-      controlSocketPathV6 = "/run/kea/dhcp6.sock";
+      controlSocketPathV4 = "/run/kea-dhcp4/dhcp4.sock";
+      controlSocketPathV6 = "/run/kea-dhcp6/dhcp6.sock";
     in
     {
       exporterConfig = {