In conflict window, add an option for creating a branch with current changes

## Description
In the conflict screen, we currently have options for saving changes to a zip file. We could add another option for saving the changes to a new branch, so that service owners can merge changes in Gitea or locally.

Here we can add another option "Jeg vil ha en ny gren med mine endrede filer".

The issue names the conflict screen and its existing option for saving changes to a ZIP, but no files, tests, or entry points. Start by locating the conflict-screen implementation and the current ZIP-save flow. Done means a new option creates a branch containing the current changes and supports the described merge workflow.

Written by the indexing model from the issue text.