Enable tab completion in datafusion-cli

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

It would be convenient if SQL keywords (and perhaps also table names, column names, etc.) were auto-completed when hitting tab within datafusion-cli, with optional formatting to upper or lowercase depending on the user's preference.

**Describe the solution you'd like**

Implement tab completion for SQL keywords.

**Describe alternatives you've considered**

None

**Additional context**

None

Start by locating the datafusion-cli input-handling and line-editing entry points, then determine how SQL keywords are represented and how completion results can be formatted. Done means tab completion works for SQL keywords in datafusion-cli, with the requested case preference if that behavior is retained.

Written by the indexing model from the issue text.