AWS::Organizations::Account Tag Dynamic Reference Support

## 1. Title

AWS::Organizations::Account Tag Dynamic Reference Support

## 2. Scope of request

In the same vein of support for [dynamic resolvers for SSM and Secrets Manager](https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/dynamic-references.html), and similar to what was suggested in #650, it would be awesome if support for dynamic resolution of account tags was added to CloudFormation.

Why do this versus just utilizing SSM/Secrets Manager? This would save us the trouble of having to provision SSM / Secrets Manager resources, provision access to said resources to deploy or modify them, and ultimately have to add statements to SCPs to protect said resources inside the accounts. Additionally cuts down on the number of parameters having to be created / managed in the master account of Landing Zone implementations.

## 3. Expected behavior

Similar to an SSM or Secrets Manager dynamic resolver, an account tag key can be passed to the resolver and the value would be returned for usage anywhere in the CloudFormation template it is allowed.

## 4. Suggest specific test cases

Further account metadata injection into CloudFormation resource naming and policies (IAM, Resource) at deploy time that is not available via Pseudo parameters today.

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

https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/dynamic-references.html
AWS Landing Zone implementations of SSM usage.

## 6. Category (required) - Will help with tagging and be easier to find by other users to +1

Other (IoT, Migration, Budgets...)

## 7. Any additional context (optional)

N/A