Rename master to main

As a developer I would like to follow github's standard for repository branch names and update the "master" branch to "main" (https://www.techrepublic.com/article/github-to-replace-master-with-main-starting-in-october-what-developers-need-to-know/).

## Acceptance Criteria
* On all our repos "master" is updated to "main"
* The "master" folder in our file structure is renamed to "main"
* Any code relying on the fact that there is a "master" branch is updated