Allow ResultsProjection to rename columns

ResultsProjection currently allows to pick which variables should be exposed in the SQL results, but the names cannot be picked by the user. It would be convenient to allow the user to choose those names, and that can be easily implemented by supporting renaming columns in ResultsProjection.

See the original feedback:

Variable names: orbital notes for input variables that . has a different semantic meaning in SQL so changes . to _. It would be nice to automatically do this for the output also (e.g. output_probability_0) or even to allow for custom names (in the case where one is ultimately tracking multiple models)

It has to be noted that the purpose of Orbital is now to implement a full query language, so for more complex cases than just renaming it just makes sense to push users toward using translate and then apply any further Ibis transformation they want instead of directly using export_sql

Start at the ResultsProjection implementation and trace how translate and export_sql produce output column names. Define completion as allowing users to choose result-column names while preserving the existing selection behavior and leaving more complex transformations to translate and Ibis.