Feature/refactor health do files

[andrewbaxter439]

What

• closes Re-organise do files #340 and Simplifying Stata v-cov matrix writing code #358
• Updates do file code to estimate health and wellbeing regressions
• also updates programs.do to take workbook argument

Why

• implements new code to make tidier, easier to run and less error-prone

[andrewbaxter439]

This is created as a draft for now to demonstrate upcoming changes. Still needs applied to the rest of the health and wellbeing outcomes but proof in principle here for the financial distress module.

@dav-sonn this also implements suggested changes from #358 and the programs.do file taking the workbook argument so it can be used across multiple things. Can be ongoing conversation to make sure all working!