This code adds a simple endpoint to apply patches to repositories and
branches on gitea. This is then used along with the conflicting checking
code in #18004 to provide a basic implementation of cherry-pick revert.
Now because the buttons necessary for cherry-pick and revert have
required us to create a dropdown next to the Browse Source button
I've also implemented Create Branch and Create Tag operations.
Fix #3880
Fix #17986
Signed-off-by: Andrew Thornton <art27@cantab.net>
