[proposal] Warn google_binary_authorization_attestor_iam for conflicting

[wata727]

See https://www.terraform.io/docs/providers/google/r/binary_authorization_attestor_iam.html

Note: google_binary_authorization_attestor_iam_policy cannot be used in conjunction with google_binary_authorization_attestor_iam_binding and google_binary_authorization_attestor_iam_member or they will fight over what your policy should be.

Note: google_binary_authorization_attestor_iam_binding resources can be used in conjunction with google_binary_authorization_attestor_iam_member resources only if they do not grant privilege to the same role.

[PatMyron]

related: #24, #26, #27, #28, #29, #31, #32, #33, #34, #35

[PatMyron]

@wata727 thoughts on closing the linked issues and tracking them all in this issue? Expanding to cover the whole list of resource types should be very quick once there's code working for any individual one of these resource types

[wata727]

Looks good. This is an idea I created from caveats in the Terraform doc, and I think it would be a good idea to create a new meta issue and close these issues.