Add create merge checkbox.

Open Jacob Schatz requested to merge new-mr-repo-editor into master

What does this MR do?

Adds a checkbox to start a new MR from a branch. Merge first. This relies upon it.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

Screenshots (if relevant)



Does this MR meet the acceptance criteria?

What are the relevant issue numbers?

Fixes #38626

Edited by username-removed-892863