RE: Enhance 'pg_createsubscriber' to retrieve databases automatically when no database is provided.

Dear Shubham,

Thanks for updating the patch! I feel the patch has good shape. Here is a small comment.

```
+       /* Error if no databases were found on the source server */
+       if (num_rows == 0)
+       {
+               pg_log_error("no databases found on the source server");
+               pg_log_error_hint("Ensure that there are user-created databases on the source server.");
+               PQclear(res);
+               disconnect_database(conn, false);
+               exit(1);
+       }
```

I think the error message is not accurate. This error can happen when there are
user-created database but it is created as template. How about below:

```
-               pg_log_error("no databases found on the source server");
-               pg_log_error_hint("Ensure that there are user-created databases on the source server.");
+               pg_log_error("no convertable databases found on the source server");
+               pg_log_error_hint("Ensure that there are non-template and connectable databases on the source
server.");
```

Best regards,
Hayato Kuroda
FUJITSU LIMITED