Support deltalake

[avantgardnerio]

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

I would like to be able to register external table stored as deltalake and select from it.

Describe the solution you'd like

See above.

Describe alternatives you've considered

1. Don't allow users to use deltalake
2. Have them hard-code support

[milenkovicm]

latest ballista can be extended to support delta table, an example can be found at https://github.com/milenkovicm/ballista_delta