Stack level tags are not applied to AWS::DocDB::*

## 2. Scope of request

c) new attribute for an existing resource is desired

Deploy a new stack with stack level tags, all DocDB resources are not tagged by stack level tags after deploying the stack.

Below is quoted from CloudFormation console,

> Stack-level tags will apply to all supported resources in your stack. You can add up to 200 unique tags for each stack.

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

https://docs.aws.amazon.com/documentdb/latest/developerguide/tagging.html

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

Use the categories as displayed in the AWS Management Console (simplified):

3. DB (RDS, DynamoDB...)

Start with the AWS CloudFormation issue and the linked Amazon DocumentDB tagging documentation. Reproduce the reported behavior by deploying a stack with stack-level tags and AWS::DocDB::* resources; done means the supported DocDB resources receive the stack-level tags.

Written by the indexing model from the issue text.