allow creation of ssm documents

## :rocket: Feature Request

### General Information
* [ ] :wave: I may be able to implement this feature request
* [ ] :warning: This feature might incur a breaking change

### Description
Currently to create a ssm document in cdk you can only use a json object as the content

```
with open('ssm/removal.json', 'r') as f:
removalDoc = json.load(f)

aws_ssm.CfnDocument(
self,'ssmdoc',
content=removalDoc,
document_type="Automation"
)
```

### Proposed Solution
Allow creating of ssm documents in cdk. ability to generate a full document with parameters etc

### Other information
I believe this is not on the roadmap for the ssm team but want to capture this so more eyes are on it

No file or test is named; start by tracing the aws_ssm.CfnDocument content API and the Python example using json.load. Clarify the supported full-document shape, then verify that an SSM Automation document with parameters can be created; the issue does not identify a test or implementation entry point.

Written by the indexing model from the issue text.