Support for rebase in git-commit step

[tarunwadhwa-paypay]

This is a suggested enhancement. There can be concurrent jobs running and it is possible that there can some git conflicts when multiple job are updating same repo.

The idea is to add support for rebasing before pushing. An argument 'rebase' can be used to toggle this behaviour.

P.S I can work on this if you think this aligns with the philosophy.