Request: a beginner-friendly branching method, new branch goes on fork

[wolftune]

Feature Description

In #20880, I described the problem with keeping a fork's main branch updated to the origin's main within the Web UI.

Here is an alternative or complementary (and potentially superior) design:

• Allow a non-team-member to edit files from a repository
  • currently the edit function is just greyed out
• When they are making their commit, only offer the option of committing on their fork (making a fork if it doesn't exist yet)
• Default to making it on a branch with a new name (not to main)
• Offer the option of opening a pull-request from their fork/branch to the origin/main

Put another way: instead of blocking users from editing directly on projects where they don't have permission to open branches, the user experience should be this: while the user is looking at a project, just let them edit and automatically make the edit go to a new branch on their fork (prompting them to confirm the creation of a fork if none was yet made).