lavinmq: the broker TLS directory is the operator's, read by whoever needs it

The controller now accesses /var/lib/mesh-broker-tls (mesh-controller
#54) and the push refused whole: lavinmq declared the directory as an
owned resource, and shared data is the operator's, owned by no module
(ADR 0051). lavinmq only ever reads the certs — genesis laid them down
— so it declares a read access like the controller does, and the
directory belongs to nobody.

modules/lavinmq/module.json

@@ -81,12 +81,6 @@
       "path": "/var/lib/mesh-broker",
       "mode": "0700"
     },
-    {
-      "id": "broker-tls",
-      "type": "directory",
-      "path": "/var/lib/mesh-broker-tls",
-      "mode": "0700"
-    },
     {
       "id": "server",
       "type": "container",
@@ -147,5 +141,11 @@
         "from": "Dockerfile"
       }
     ]
+  },
+  "accesses": [
+    {
+      "path": "/var/lib/mesh-broker-tls",
+      "mode": "read"
     }
+  ]
 }