feat: add case sensitivity option for generate_model_yaml column names

[guilhem-dvr]

resolves #

Problem

Column name case matters in yaml files - for instance when enabling constraints on a model. With a sufficiently many columns, you start to wish for this option to exist...

This addresses #175.

Solution

This CL adds an optional parameter to the generate_model_yaml macro to switch case sensitivity when generating model column names.

Checklist

• This code is associated with an issue which has been triaged and accepted for development.
• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• I have updated the README.md (if applicable)