Ensure external principals are allowed for AWS RAM resources

AWS RAM resource share has 'allows external principals' disabled which may cause your entire organization or organizational units to lose access to the shared resources.

In AWS Console -

1. Sign in to the AWS Console and go to the shared by me page on AWS RAM Console.
2. Select the appropriate Region.
3. Select Modify.
4. Go to the 'Allow sharing with external principals' page by clicking next and set it as 'Allow sharing with external principals.'.
5. Review and Update.

In Terraform -

1. In the aws_ram_resource_share resource, set 'allow_external_principals' to 'true'.

References:
https://docs.aws.amazon.com/resource-explorer/latest/userguide/security_iam.html
https://registry.terraform.io/providers/hashicorp/aws/latest/docs/resources/ram_resource_share#allow_external_principals