nextcloud: deliver the admin password to the sidecar too

The sidecar's own client needs MESH_NEXTCLOUD_ADMIN_PASSWORD to list
shares over the OCS API, but the runtime container's env/volumes never
carried it -- only the server container did. Delivered the same way every
other sealed value in this manifest already is: a generated env-file with
the ${secret:admin} substitution, not a raw value in the container's env.

modules/nextcloud/module.json

@@ -98,6 +98,13 @@
       "content": "{}\n",
       "merge": "json"
     },
+    {
+      "id": "runtime-admin-env",
+      "type": "file",
+      "path": "/var/lib/mesh/nextcloud/admin.env",
+      "mode": "0600",
+      "content": "MESH_NEXTCLOUD_ADMIN_PASSWORD=${secret:admin}\n"
+    },
     {
       "id": "runtime",
       "type": "container",
@@ -108,6 +115,9 @@
         "/var/lib/mesh/nextcloud/config.json:/run/config/config.json:ro",
         "/var/run/docker.sock:/var/run/docker.sock"
       ],
+      "env-file": [
+        "/var/lib/mesh/nextcloud/admin.env"
+      ],
       "env": {
         "MESH_BROKER_FILE": "/run/secrets/broker",
         "MESH_NEXTCLOUD_URL": "http://127.0.0.1:80",