deploy: move the queue toggle

Same shape as the others. Three of the eight references were prose
rather than code: two assertion messages naming the option to an
operator, and a `defaultText` in the authelia module, whose
`oidc.hiveIdentities` derives from whether the queue runs here.

Also corrects a comment in swarm.nix that this commit's own hunk sits
directly beneath. It said `enableRequiredServices` turns on matrix and
authelia "but NOT nats (nats has no mode that enables it)", which stopped
being true when the queue was added to that switch — before this change,
not by it. The reasoning it introduces is still right and still worth
keeping; only the premise had expired.

nix/host-modules/deploy.nix

@@ -57,6 +57,10 @@ in
       [ "services" "hyperhive" "swarm" "authelia" "enable" ]
       [ "services" "hyperhive" "deploy" "authelia" ]
     )
+    (lib.mkRenamedOptionModule
+      [ "services" "hyperhive" "swarm" "nats" "enable" ]
+      [ "services" "hyperhive" "deploy" "nats" ]
+    )
   ];
 
   options.services.hyperhive.deploy = {
@@ -119,6 +123,19 @@ in
       '';
     };
 
+    nats = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      description = ''
+        Run the swarm's message queue in a `swarm-nats` container on this
+        host. A swarm has one queue, so this belongs on the same host as
+        the rest of the shared services.
+
+        Off by default, and off means *absent*: no container is created
+        and nothing else in the evaluated config changes.
+      '';
+    };
+
     controller = lib.mkOption {
       type = lib.types.bool;
       default = false;