ENH: add support for child teams

[bsipocz]

Child teams could be very useful for keeping access clean and structured. E.g. each repo will have a maintainers team with an admin child team. With this approach I expect it to be easier to audit e.g. if every repo has at least write access by at least 2 people, etc.

[stefanv]

https://docs.github.com/en/rest/teams/teams?apiVersion=2022-11-28#create-a-team