Migrate audit-logger: it builds itself now

The first module moved onto the new build process. It named a placeholder digest
nothing could produce, so it only ever worked where somebody had pre-built its
image by hand. It names the two shared bases instead, and the mesh builds it.

Chosen first deliberately: it requires nothing, nothing requires it, and an
audit trail of every event on the mesh is the thing most worth having while
modules are being moved one at a time.

modules/audit-logger/module.json

@@ -2,10 +2,33 @@
   "module": "audit-logger",
   "version": "1",
   "slug": "audit",
-  "consumes": ["#"],
+  "consumes": [
+    "#"
+  ],
   "own-secrets": {
     "broker": "/var/lib/audit-logger/broker"
   },
+  "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"
+      }
+    ]
+  },
   "resources": [
     {
       "id": "state",
@@ -23,7 +46,6 @@
       "id": "run",
       "type": "container",
       "name": "mesh-audit-logger",
-      "image": "mesh-runtime-audit@sha256:0000000000000000000000000000000000000000000000000000000000000000",
       "network": "host",
       "volumes": [
         "/var/lib/audit-logger/broker:/run/secrets/broker:ro",
@@ -32,7 +54,8 @@
       "env": {
         "MESH_BROKER_FILE": "/run/secrets/broker",
         "AUDIT_LOG": "/trail/audit.log"
-      }
+      },
+      "artifact": "runtime"
     }
   ]
 }