codeowner havoc on stack submit

Suppose we restack a stack and then submit changes to github with `gs stack submit`. This sometimes has a side-effect of many code-reviewers being auto-requested due to codeowner configurations in github.

I was wondering if it would be possible to avoid this by switching all PRs in a stack to/from draft mode before/after pushing changes as part of a `stack submit`? For example, on calling `gs stack submit`, I would want git-spice to switch all PRs in the stack to draft mode, proceed with `stack submit` as usual, and finally return all PRs back to their original draft/non-draft state.