Add more git push options

This is a follow up to https://gitlab.com/gitlab-org/gitlab-ce/issues/43263 and https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26752 which added the following push options:

• -o merge_request.create
• -o merge_request.target=branch1
• -o merge_request.merge_when_pipeline_succeeds

The new push options that would be useful on top of the above are:

• -o merge_request.should_remove_source_branch
• -o merge_request.title
• -o merge_request.description

I am asking for the above in behalf of @avar who is currently away.

I realized that there is already -o ci.skip (see https://docs.gitlab.com/ee/ci/yaml/#skipping-jobs), so as far as I understand there is no need for -o merge_this_right_away that was suggested.

This is related to: https://gitlab.com/gitlab-org/gitlab-ce/issues/5942