Include IAM policy to validate phone numbers

**Description:**
As soon you deploy a new lambda using SAM CLI, you get a validation erro due to the policy ARN to validate phone numbers from pinpoint service is not available as a AWS managed permission.

**Steps to reproduce the issue:**
1. Go to AWS IAM console
2. Search for PinpointReadAccess
3. Use that policy in the list of policies inside you yaml file
4. Try to deploy

**Observed result:**
400 status code

**Expected result:**
200 OK for the function iam role stack

I have a proposal of a PR here:
https://github.com/awslabs/serverless-application-model/pull/1466