Added permissions for the custom query file

Adding an entry for permissions needed by the last query in the custom query file. The last query allows for query-level metrics and is critical for some customers.

src/content/docs/infrastructure/host-integrations/host-integrations-list/postgresql/postgresql-integration.mdx

@@ -165,6 +165,20 @@ If you also want to obtain table and index-related metrics (for example, table s
 GRANT SELECT ON ALL TABLES IN SCHEMA public TO new_relic;
 ```
 
+If you also want to obtain query-level metrics from the Postgres custom query config file, the PostgreSQL role used by the integration (`new_relic`) also needs to be added to the (`pg_read_all_stats`) role. This is due to the user leveraging the (`pg_stat_statements`) extension. This extension may require additional steps mentioned in the (`Additional notes`) section below.
+
+```
+GRANT pg_read_all_stats TO new_relic;
+```
+
+Additional notes:
+
+- **Enabling the Extension** Enabling the pg_stat_statements extension may require you to manually create it from a query prompt.
+
+```
+CREATE EXTENSION pg_stat_statements;
+```
+
 ### postgresql-config.yml sample files [#examples]
 
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