Proposal to add commitOptions to git config -- Update GitAdapter.groovy

[loosebazooka]

Proposal for adding git commit options.

This means a user can do something like ["-s"] to satisfy DCO bots: https://github.com/apps/dco

[Hillkorn]

Makes sense to me to add this. Can you add it to the README and write tests for it please.
Thought about an explicit config for signing like we have for tags but I personally prefer a generic option.

[loosebazooka]

Thought about an explicit config for signing like we have for tags but I personally prefer a generic option.

To me there's a very strong difference between "signing" and "signing-off" here. I'm mostly concerned with -s "sign-off" to satisfy the DCO bot, but I think the word "signing" would more align with -S.

I'll keep this generic for now.