Keep the original SQL for CreateExternalTable::definition

### Is your feature request related to a problem or challenge?

Currently, the CreateExternalTable definition is just a stringified version of the statement, rather than the original SQL that was parsed.

### Describe the solution you'd like

I'd like to propose capturing the original SQL as provided and storing that instead so that when a definition is displayed, it matches what a user originally provided.

### Describe alternatives you've considered

Nothing comes to mind. Its a fairly small change.

### Additional context

_No response_

Start by locating CreateExternalTable::definition and follow how the statement is parsed and its definition is stored. Check the existing tests around CreateExternalTable display or parsing, then verify that the displayed definition preserves the SQL originally provided rather than a stringified statement.

Scritto dal modello di indicizzazione a partire dal testo della issue.