Rename default "master" branch to "main"

I would like to suggest the renaming of the project's default branch `master` to `main`, following Git's defaults. A brief summary of the recent developments regarding the shift towards `main` instead of `master` is given in these articles of [GitLab](https://about.gitlab.com/blog/2021/03/10/new-git-default-branch-name/) and [GitHub](https://github.com/github/renaming). I think only @henrikingo currently has the permissions to do so. Any chances we can change this?

Start by reviewing the repository's default-branch settings and the GitHub branch-renaming guidance linked in the issue. Check what repository references or workflows depend on the current branch name; done means the default branch is `main` and affected references continue to work.

Written by the indexing model from the issue text.