Add setting to change default values for Web IDE commit options
### Problem to solve
On the GitLab instance I manage, I have many projects that do not need any workflow management. For these projects, merge requests and branches are a hindrance. I frequently edit these projects via the Web IDE. The the fact that "Start a new merge request" defaults to checked and the branch radio defaults to "Create a new branch" is ***incredibly*** frustrating because I **never** want to do either of these.
### Intended users
* [Sasha (Software Developer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sasha-software-developer)
* [Devon (DevOps Engineer)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#devon-devops-engineer)
* [Sidney (Systems Administrator)](https://about.gitlab.com/handbook/marketing/product-marketing/roles-personas/#sidney-systems-administrator)
### Proposal
Add a setting at the project level and at the group level that allows users to override these defaults.
### What does success look like, and how can we measure that?
I can override these default values.
issue