[work in progress] Add ability to set checks field in required_status_checks of github_branch_protection_v3

[k24dizzle]

Attempt to solve #985 for github_branch_protection_v3.

According to the docs, the checks field contains a list of objects that contain the fields of context and app_id.

Note: I wrote a unit test to test out the checks field, but not sure how to actually run it to make sure this code works.