bootstrap: planned object-storage reef, no rail

Declare reef-storage as substrate_kind object-storage. Hold non-secret
attribute paths for Scaleway S3. Do not host a compute rail.

substrate/object-stores/platform-audit-storage.yaml

@@ -0,0 +1,15 @@
+# Planned. Fill after RESOURCE-WP-0002 purchase. No secrets.
+schema_version: "0.1"
+resource_id: resource:platform:audit-storage
+provider: Scaleway
+status: planned
+endpoint: null
+region: null
+bucket: null
+prefix: null
+versioning: null
+lifecycle: null
+provider_project_ref: null
+notes:
+  - Destination for rapp-postgres WAL and base backups once procured.
+  - resource-control cites reef:storage/substrate/object-stores/platform-audit-storage.yaml#<key>