Support to "alwaysSignOff" commits (via a preference)

[JonasHelming]

When pressing CTRL+ENTER in the SCM view, the commit is done without "signoff". You can commit with signing off via the hamburger menu, though. As a user, i would like a setting, where I can turn on "autosignoff" so the CTRL+ENTER always also signs off. we will push a contribution implementing this

[JonasHelming]

Pull request: #6402

[JonasHelming]

There is now a setting git.alwaysSignOff. If you turn it to true, all commits, triggered via CTRL+ENTER or via the manu are always signed off.