review/rework "generate_field_definitions" function

[andrewcstewart]

This function was lifted from an example as a first pass at inferring the schema for generating the Hive table definition. Unfortunately it is fairly buggy and a workaround currently renders every field as a string.

Hive table field definitions should conform to https://docs.aws.amazon.com/athena/latest/ug/data-types.html