Allow me to set a merge s="ours" point in the auto-merge chain

In the merge dialog, Stash shows a list of the branches it's about to auto-merge into.

There are some cases where you want to prevent those changes from being merged into a release branch - perhaps because there has been a refactor in a particular release and a different fix was applied already (or will be applied in the future by another branch and PR).

This suggestion is for the ability to elect a branch where the change will stop propagating. The automerge will still technically propagate through all releases, but it will be a no-op change into that branch and all branches after it because the merge will be done with the "strategy=ours" option set.