Add support for Github Flow

I know that Lazygit supports Git Flow, but a few months after support was added, the author of the original Git Flow document [said that he no longer recommends his approach](https://nvie.com/posts/a-successful-git-branching-model/), saying:

> This is not the class of software that I had in mind when I wrote the blog post 10 years ago. If your team is doing continuous delivery of software, I would suggest to adopt a much simpler workflow (like [GitHub flow](https://guides.github.com/introduction/flow/)) instead of trying to shoehorn git-flow into your team.

I couldn't find any direct reference to Github Flow in other issues, so I thought I'd raise it as something could possibly be supported in the presence of the Github CLI tool.

Is this something that's worth adding to the roadmap?