Inventory: restructure folders

lib/inventory/spec/schema/schema.cue

@@ -0,0 +1,39 @@
+package schema
+
+#machine: machines: [string]: {
+    name: string,
+    description?: string,
+    icon?: string
+    tags: [...string]
+}
+
+#role: string
+
+#service: services: [string]: [string]: {
+    // Required meta fields
+    meta: {
+        name: string,
+        icon?: string
+        description?: string,
+    },
+    // We moved the machine sepcific config to "machines".
+    // It may be moved back depending on what makes more sense in the future.
+    roles: [#role]: {
+        machines: [...string],
+        tags: [...string],
+    }
+    machines: {
+        [string]: {
+            config?: {
+                ...
+            }
+        }
+    },
+
+    // Configuration for the service
+    config: {
+        // Schema depends on the module.
+        // It declares the interface how the service can be configured.
+        ...
+    }
+}