add option to use --signoff with git commit

[pvogt09]

This PR adds the ability to --signoff the created commit by introducing a new options signoff.

[EndBug]

Hi, thanks for the PR, but I have some questions:

• I've run a couple of tests with your code, and it doesn't seem to commit correctly. Could you link me to the tests you ran so that I can confront them?
• The new option would only add an argument to the git add command, wouldn't it be easier to just add it in the add option (like src --signoff)? If not, are there any issues in doing so?

I know that the --force parameter has its own option in this action, but I feel like it would be better to just add a field that you can use to put your custom options, if that can't already be achieved by using the add field.

[pvogt09]

I have tested it by changing the build.yml to use the local version of the action and the result was https://github.com/pvogt09/add-and-commit/actions/runs/187259492/workflow which passed and created a commit with the desired commit message and "Signed-off-by" line. For the PR I deleted these commits again and force pushed a more tidyer version. I just recreated the local test in https://github.com/pvogt09/add-and-commit/tree/test.

The aim of the signoff flag is not to change git add (that does not have a --signoff argument btw), it is supposed to add "Signed-off-by: author < email-address >" to the commit message (like in 0cbe3c6). It might be possible to archieve the same with the message option, but then author and email of the push/pull_request that started the workflow have to be known in advance and can not be changed/dynamically derived.

[EndBug]

Sorry, my bad:

• When I meant that it wasn't committing correctly I meant that it didn't do it correctly when the option was not being used.
• You're right, that goes to the git commit command, using a dedicated option is ok

[EndBug]

I think the problem was caused by the fact that you used double quotes with the sign off variable.
I've also refactored the code to make it look like the add function.

You're welcome to give it a check, if that works for you I'll publish it in the next minor version ;)

[pvogt09]

I am ok with the changes. Thank you for the help.

[EndBug]

@all-contributors please add @pvogt09 for code

[allcontributors]

@EndBug

I've put up a pull request to add @pvogt09! 🎉

[EndBug]

Ok, you can find the new feature in version v4.3.0 (available also using v4 and latest)

Thanks again for your contribution ✨