push: the wait is the call's or the controller's setting push-wait, never a length in the code (issue 629)

The operator's rule: a wait is never hard-coded, at most a default is configured. The push verb takes `wait`; without it the controller's setting `push-wait` (module default 2m) applies; a setting that cannot be read waits for nothing, as a push did before, and says so.

module.json

@@ -35,6 +35,11 @@
       "kind": "preference",
       "default": "10m",
       "why": "a busy period never holds a batch longer than this after its first merge (novox/hq ADR 0276)"
+    },
+    "push-wait": {
+      "kind": "preference",
+      "default": "2m",
+      "why": "how long a push to a named machine waits for that machine's answer, so its call says how it went; a call's own wait overrides it, and 0 waits for nothing (novox/hq issue 629)"
     }
   },
   "tools": [
@@ -120,6 +125,14 @@
       "owner": "mesh-controller",
       "content": "{\n  \"merge-window\": \"${setting:merge-window}\",\n  \"merge-window-at-most\": \"${setting:merge-window-at-most}\"\n}\n"
     },
+    {
+      "id": "push",
+      "type": "file",
+      "path": "${dir:mesh-state}/push.json",
+      "mode": "0600",
+      "owner": "mesh-controller",
+      "content": "{\n  \"push-wait\": \"${setting:push-wait}\"\n}\n"
+    },
     {
       "id": "controller",
       "type": "process",
@@ -144,7 +157,8 @@
         "MESH_BROKER_ADDRESS_PORT": "${seat:mesh-broker:5671}",
         "MESH_BUS_NATS_FILE": "${dir:mesh-state}/bus",
         "MESH_CONTROLLER_VERSION": "${version}",
-        "MESH_MERGE_WINDOW_FILE": "${dir:mesh-state}/merge-window.json"
+        "MESH_MERGE_WINDOW_FILE": "${dir:mesh-state}/merge-window.json",
+        "MESH_PUSH_FILE": "${dir:mesh-state}/push.json"
       },
       "replaces": [
         "server"