Git supports push options since v2.10.

They can be set on CLI, (-o) or using the push.pushOption config.

Please add support for this in libgit2 and pygit2.

Refs:

• Git's client-side push options: git/git@f6a4e61
• Gitlab's server-side push options: https://docs.gitlab.com/ee/user/project/push_options.html#push-options