Git commit using '--signoff'

[FabianLauer]

This PR addresses issue #7010. It adds support for committing with the --signoff flag enabled.

Instead of using a checkbox under the commit message input as suggested by @FrenchBen in the original issue, I added 2 actions to the context menu since signed off commits are fairly rare.

[msftclas]

Hi @FabianLauer, I'm your friendly neighborhood Microsoft Pull Request Bot (You can call me MSBOT). Thanks for your contribution!

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[msftclas]

@FabianLauer, Thanks for signing the contribution license agreement so quickly! Actual humans will now validate the agreement and then evaluate the PR.

Thanks, MSBOT;

[joaomoreno]

Thanks!

[FabianLauer]

Awesome, thanks! 😃
I hope I didn't cause you more work than the PR saved, looks like you made quite a few changes in these files afterwards 😳

[joaomoreno]

No no, thank you! It was pretty great already, I simply did small refactorings. Most importantly, I made a protected abstract commit() on the BaseCommitAction, which lets us reuse most of the code between all those actions. 👍

[FabianLauer]

Great, thanks for the insight, very helpful 😃