Give the user better information about which tables are not in the wrds module but exist in SAS

[cc8734]

The issue was discussed in Slack here, please refer to it as it is a more in-depth discussion on the topic: https://wharton.slack.com/archives/C0WU8LUCE/p1734446424640739

Summary: While using the wrds module, if the data is in SAS but not in Postgres, the wrds module does not clearly communicate this. For example if using the list_tables method, it throws a NotSubscribedError. Errors messages like these create confusion and this is a common user question on Zendesk. We could do a better job to inform users in the error message(s) that the table being queried does exist, but it only exists in SAS and therefore cannot be accessed using the wrds module.

An ideal solution would reduce user confusion, but also be stable and little effort to maintain.