Setup common git config options for KDE project repositories
Some Git options may be useful for KDE's repositories and should be set by default. Along the lines of the existing support for options like
user.email (which is already set globally but perhaps is better per-repo).
Especially if we shift to Gitlab where branches will be created and deleted frequently, enforcing the use of
--prune when we do
git fetch in kdesrc-build would be a prudent default.
Of course, would need to be optional in case the user knows better than we do.