Automatically register tables if ObjectStore root is configured

[avantgardnerio]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.

It is not convenient for users to always issue SQL DDL commands to register tables upon each session initiation. In my company's case, data is automatically persisted to deltalake on s3, and when analytical queries are sent to Ballista, it would be difficult for the consuming JDBC application to track and register all the unregistered tables upon each connection event.

This is also true of users of BI tools, such as Tableau, which expects to:

1. connect
2. enumerate tables using JDBC
3. drag-and-drop existing tables into a workspace

Tableau lacks the functionality to even run a query to register a table before the tables have been enumerated.

Describe the solution you'd like

Add datafusion configuration values for datafusion.catalog.location and datafusion.catalog.type so that users of DataFusion (such as Ballista) can set these values (from environment variables) to automatically scan the ObjectStore and add any tables as appropriate, so that they automatically appear for consumers such as Tableau.

Describe alternatives you've considered

Insist consumers always run register external table commands each time they connect.