Support deltalake

**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

The issue names no files, tests, or entry points. Start by locating external-table registration and table-provider support, then determine how Delta Lake tables should be discovered and queried. Done means users can register an external Delta Lake table and select from it without hard-coded support.

Written by the indexing model from the issue text.