Improve github team resource

[bpaquet]

Fix various issue with the github_team resource

• During import, set create_default_maintainer to false to avoid a diff in the resource. This parameter is not used outside of the Create method
• Improve the handling of parent_team_id. This parameter is complicated to manage because it can be an ID or a slug, and the current behaviour is not correct (no cast from Int to String when the parameter is Set in the Read function). A cleaner way to do things is to have two parameters parent_team_id and parent_team_slug for example. But I do not want to introduce compatibility issues, so that's why this PR
  • Cast the ID to string when the Read function set it
  • Create two new computed params, which store the slug name and the ID in two different parameters
  • Ignore diff on parent_team_id if this paremeter match one of the two low level params.

With these modifications, I'm able to import a team, with a parent id, and having no diff in a following plan.

Integration tests are still green.

[kfcampbell]

Thank you @bpaquet! Confirming all integration tests are passing for me as well.