allow drafting

[oscar-chevalier]

Hello,

This PR allows to create drafts from the API.
Documentation: https://docs.github.com/en/rest/pulls/pulls?apiVersion=2022-11-28#create-a-pull-request
Thank you in advance.

[kit-ty-kate]

That change in itself seems alright (modulo the comment), however as a github-data user, i find it a bit annoying to have the library break for a lot of (most?) users, for such a small change.

Could you at least add the rest of the optional fields so that we at least don't have to change that type again in the foreseeable future?

[oscar-chevalier]

Hello,

Thank you for the review.
Also, according to #184, maintainer_can_modify should be true by default.

Should head_repo be a string option like body?

[kit-ty-kate]

Should head_repo be a string option like body?

I believe so, yes.

After looking around at #168 and atdgen -v i'm hoping to merge this at the same time as the new Github_v module in github-data so that a future-proof constructor exists somewhere, to avoid more breakages in the future.