cbimport: support simple transformation on the fields used to generate the key

Background
This request was raised on the forums

Problem
Some times the field(s) used to generate the key by cbimport are in mixed case and the user would like it to be lower or uppercase.

Expectation
It would be useful if cbimport supported simple transformation on the fields used to generate the key

• All to lower case
• All to upper case
• first char to upper case.