Add a new git.auto-local-branch config option. When set to false, a
remote-tracking branch imported from Git will not automatically create a
local branch target. This is implemented by a new GitSettings struct
that passes Git-related settings from UserSettings.
This behavior is particularly useful in a co-located jj and Git repo,
because a Git remote might have branches that are not of everyday
interest to the user, so it does not make sense to export them as local
branches in Git. E.g. https://github.com/gitster/git, the maintainer's
fork of Git, has 379 branches, most of which are topic branches kept
around for historical reasons, and Git developers wouldn't be expected
to have local branches for each remote-tracking branch.
