Allow specifying git push options for image automation controller

[Maistho]

Git has the ability to add options that are sent to the server when pushing: https://git-scm.com/docs/git-push#Documentation/git-push.txt--oltoptiongt

Gitlab can use these options to automatically create a merge request when pushing https://docs.gitlab.com/ee/user/project/push_options.html#push-options-for-merge-requests

Allowing users to set push options for the image automation controller would make creating merge requests with Gitlab really easy.