Defer minio from the buildable set too (issue 060)

minio's runtime copies the `mc` client from minio/mc:latest — a
Docker Hub pull the mesh build environment cannot make (its docker
reaches the mesh registry, not public Hub), the same isolation that
blocks npm deps. apt-based installs (mongodb's mongosh, mosquitto)
build fine because the build has real internet for apt; only npm and
Docker Hub are redirected. Delivering an external binary or image layer
into a mesh build is the same open question as the npm deps — deferred
with them.

modules/minio/module.json

@@ -102,6 +102,7 @@
       "id": "runtime",
       "type": "container",
       "name": "mesh-minio",
+      "image": "mesh-runtime-minio@sha256:0000000000000000000000000000000000000000000000000000000000000000",
       "network": "minio",
       "volumes": [
         "/var/lib/mesh/minio/broker:/run/secrets/broker:ro",
@@ -114,29 +115,7 @@
         "MESH_MINIO_ROOT_PASSWORD_FILE": "/run/secrets/root",
         "MESH_BROKER_FILE": "/run/secrets/broker",
         "MESH_RECEIVES": "/var/lib/minio/grants/mesh.json"
-      },
-      "artifact": "runtime"
+      }
     }
-  ],
-  "build": {
-    "on": [
-      {
-        "arg": "BUILD_BASE",
-        "module": "mesh-tools",
-        "artifact": "build"
-      },
-      {
-        "arg": "RUNTIME_BASE",
-        "module": "mesh-tools",
-        "artifact": "runtime"
-      }
-    ],
-    "artifacts": [
-      {
-        "name": "runtime",
-        "kind": "image",
-        "from": "Dockerfile"
-      }
-    ]
-  }
+  ]
 }