Default branch protection drop down

Proposal

Replace the form-select with a form-group that matches protected branch options.

From discussion here re-order the list to no one, maintainer, developers

Admin area

Not protected	Protected (Default)

Group

Allow owners to make changes	Only administrators can make a change
Admins always have control	Disable the group

Implementation plan

frontend weight estimated at 2️⃣

1. Update app/views/shared/_default_branch_protection.html.haml to show the new options.
2. Options set in lib/gitlab/access.rb
3. Update specs.