Respect branch.autoSetupMerge Git option #4979
Description
Is your feature request related to a problem? Please describe.
Depending on the value of branch.autoSetupMerge Git can set up the upstream/merge/integration branch (branch.<name>.merge) differently from the push branch. This is particularly useful for triangular workflows where you pull from an "upstream" remote put push to a forked "origin" remote.
For example, with the default autoSetupMerge value of true, running git branch myfeature origin/integration will create a config entry of branch.myfeature.merge = refs/heads/integration, with integration being the remote tracking branch. With autoSetupMerge = inherit you can also just run git branch myfeature while on main and Git will set branch.myfeature.merge = refs/heads/main.
Unfortunately lazygit doesn't seem to respect this option, never setting the merge option regardless of how a branch is created. Even explicitly going to the "Remotes" tab and creating a branch from one of the remote branches doesn't set that branch as the merge branch.
Describe the solution you'd like
It would be great if lazygit could respect the branch.autoSetupMerge option so that for example if it is set to inherit then just creating a new branch from, say, main will inherit its tracking branch config as expected. And when creating a branch from the "Remotes" tab is should act as if you were running git branch <name> <remote branch> to set that remote branch correctly as the merge branch.
In addition, although this may be a separate request, it would be great if lazygit could show the divergence for both the merge branch and the push branch if they are different. In this case showing the divergence from the "base" branch would probably be unnecessary since having a different merge branch already makes it explicit what the "base"/integration branch is, so the merge branch divergence could be shown in place of the current base branch divergence (the cyan arrow), and the push branch divergence could be shown in place of the current merge/upstream divergence (the yellow arrows). Hopefully this explanation wasn't too confusing.
Describe alternatives you've considered
Without this support getting the desired functionality is only really possible by running Git manually.