Chore: Automate rename master branch to main

[nelsonic]

At present most of the repos in @dwyl have the default branch set to the "legacy" master ...
Given that the industry has moved to naming default branches to main see #8
We need to automate it for the

Looks fairly easy to do: https://docs.github.com/en/rest/branches/branches#rename-a-branch

Todo

• Write function that checks each repo for the default branch name
• If the default repo is master, rename it to main
• finally protect the main branch