AWS::SNS::Permission

## 1. Title

AWS::SNS::Permission

## 2. Scope of request

AWS::SNS::Permission - can add permission to a SNS topic via API but not via CloudFormation

## 3. Expected behavior

In Create, it should add a new permission to the SNS topic policy, the same as `aws sns add-permission`
In Update, it should replace the existing permission, as if one performed `aws sns remove-permission` and then `aws sns add-permission` (since there's no `update-permission`)
In Delete, it should remove the existing permission, the same as `aws sns remove-permission`

## 5. Helpful Links to speed up research and evaluation

https://docs.aws.amazon.com/sns/latest/api/API_AddPermission.html
https://docs.aws.amazon.com/sns/latest/api/API_RemovePermission.html

## 6. Category (required)

Integration