brother: the admin account, its owned secrets, the process and the printer-asks stream declared as mesh-mail's sender is; an integration test and the README (issue 1453)

modules/brother/module.json

@@ -65,9 +65,33 @@
   "own-secrets": {
     "admin-password": {
       "path": "${dir:state}/admin-password.secret",
-      "issued-by": "outside"
+      "issued-by": "outside",
+      "prompt": "the admin password of the Brother printer",
+      "owner": "brother-admin"
+    },
+    "broker-admin": {
+      "path": "${dir:state}/broker-admin.secret",
+      "owner": "brother-admin"
     }
   },
+  "streams": [
+    {
+      "name": "printer-asks",
+      "events": [
+        "printer.asked"
+      ],
+      "max-age-days": 1,
+      "max-mib": 8,
+      "retention": "work-queue",
+      "max-deliveries": 3
+    }
+  ],
+  "state": [
+    {
+      "name": "printer-answers",
+      "ttl-seconds": 600
+    }
+  ],
   "seats": [
     {
       "name": "scanner",
@@ -114,10 +138,16 @@
     "scanner.list"
   ],
   "resources": [
+    {
+      "id": "account",
+      "type": "user",
+      "name": "brother-admin",
+      "shell": "/usr/bin/nologin"
+    },
     {
       "id": "state",
       "type": "directory",
-      "mode": "0700",
+      "mode": "0711",
       "owner": "${machine:account}",
       "place": ".",
       "unknown": "program"
@@ -127,7 +157,7 @@
       "type": "file",
       "path": "${dir:state}/settings.json",
       "owner": "${machine:account}",
-      "mode": "0600",
+      "mode": "0644",
       "takes-config": [
         "scanner",
         "scan-folder",
@@ -139,6 +169,36 @@
       ],
       "merge": "json",
       "template": "files/settings.json"
+    },
+    {
+      "id": "admin",
+      "type": "process",
+      "name": "brother-admin",
+      "artifact": "tools",
+      "run": [
+        "./brother",
+        "admin"
+      ],
+      "user": "brother-admin",
+      "env": {
+        "BROTHER_SETTINGS": "${dir:state}/settings.json",
+        "BROTHER_ADMIN_PASSWORD": "${dir:state}/admin-password.secret",
+        "BROTHER_BROKER": "${dir:state}/broker-admin.secret"
+      },
+      "restart-on": [
+        "settings"
+      ],
+      "bus": {
+        "queues": [
+          "printer-asks"
+        ],
+        "state": [
+          "printer-answers"
+        ]
+      },
+      "health": {
+        "kind": "unit"
+      }
     }
   ],
   "build": {
@@ -154,8 +214,7 @@
           "brother"
         ],
         "env": {
-          "BROTHER_SETTINGS": "${dir:state}/settings.json",
-          "BROTHER_ADMIN_PASSWORD": "${dir:state}/admin-password.secret"
+          "BROTHER_SETTINGS": "${dir:state}/settings.json"
         }
       },
       {