chore: import upstream snapshot with attribution

docs/en/integrations/spanner/prebuilt-configs/spanner-postgresql-dialect.md

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+---
+title: "Spanner (PostgreSQL dialect)"
+type: docs
+description: "Details of the Spanner (PostgreSQL dialect) prebuilt configuration."
+---
+
+## Spanner (PostgreSQL dialect)
+
+*   `--prebuilt` value: `spanner-postgres`
+*   **Environment Variables:**
+    *   `SPANNER_PROJECT`: The GCP project ID.
+    *   `SPANNER_INSTANCE`: The Spanner instance ID.
+    *   `SPANNER_DATABASE`: The Spanner database ID.
+*   **Permissions:**
+    *   **Cloud Spanner Database Reader** (`roles/spanner.databaseReader`) to
+        execute DQL queries and list tables.
+    *   **Cloud Spanner Database User** (`roles/spanner.databaseUser`) to
+        execute DML queries.
+*   **Tools:**
+    *   `execute_sql`: Executes a DML SQL query using the PostgreSQL interface
+        for Spanner.
+    *   `execute_sql_dql`: Executes a DQL SQL query using the PostgreSQL
+        interface for Spanner.
+    *   `list_tables`: Lists tables in the database.
+    *   `search_catalog`: Searches for data assets in Knowledge Catalog (Dataplex).