Retire `master` move to `main`

[hmacdope]

We should probably follow convention from main repo and here: https://github.com/github/renaming#why-main

[micaela-matta]

@namiroues do you feel like tackling this?

[namiroues]

I am working on this issue, but waiting for the merge of #464 and #458 before I change the default branch to main.