fix(deploy): clarify device postgres bootstrap plan

infra/deploy-runner/nodedc-deploy

@@ -8124,6 +8124,14 @@ def preflight_device_plane_postgres_bootstrap():
     return "absent"
 
 
+def device_plane_postgres_plan_selection(postgres_preflight):
+    if postgres_preflight is None:
+        return "preserved-prerequisite:not-selected"
+    if postgres_preflight != "absent":
+        die("Device Plane PostgreSQL plan preflight state is invalid")
+    return "bootstrap-selected:create-if-absent"
+
+
 def component_compose_root(component):
     return COMPONENTS[component].get("compose_root", component_root(component))
 
@@ -13492,7 +13500,10 @@ def plan_artifact(artifact):
         print(f"runtime_secret=runner-managed:{DEVICE_PLANE_POSTGRES_PASSWORD_FILE}")
         print(f"runtime_secret=runner-managed:{DEVICE_PLANE_GATEWAY_CORE_TOKEN_FILE}")
         print(f"runtime_secret=runner-managed:{DEVICE_PLANE_IDENTIFIER_PEPPER_FILE}")
-        print("device_postgres=preserved-prerequisite:not-selected")
+        print(
+            "device_postgres="
+            f"{device_plane_postgres_plan_selection(device_plane_postgres_preflight)}"
+        )
         print("device_postgres_volume=preserved:nodedc-device-plane-postgres-data")
         print("device_gateway_public_ingress=disabled")
         print("device_gateway_command_transport=disabled")