Support for AWS SSO IAM customer managed policies

[bruman]

Amazon just released a new feature.

https://aws.amazon.com/about-aws/whats-new/2022/07/aws-single-sign-on-aws-sso-aws-identity-access-management-iam-customer-managed-policies-cmps/

It would be awesome if this was added to the terrafrom-aws-sso module. On looking at the release is sounds like we can now add IAM customer managed policies to the SSO permission sets, so we can do stuff like use the same IAM policy on an IAM user or OIDC role as an SSO user.

[smaruy30]

terraform has the resource type.
I can make PR, I think.