when editing a file, always suggest to create a new branch

Description including problem, use cases, benefits, and/or goals

Right now, when are able to do so and click on edit, the default branch is prefilled in the branch box. Only when you edit it, a suggestion to immediately create a merge request is given.

That's great for people that are familiar with Git and GitLab, but not for everyone else. For those people, it's not logical that you'd have to manually edit the branch box before being able to create a new branch.

Initial Proposal

We always show the checkbox to create a merge request. When someone changes the branch name, we check it for them. When someone just checks it, with the branch still being the source branch, we change the branch name to something reasonable.

Links / references

@jschatz1 what do you think?