System Manager Document Provisioner

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#### Description

I would like the ability to provision an image using System Manager Documents.

#### Use Case(s)

I am strictly building images in AWS and already manage my EC2 instances using SSM. It would be useful if I could leverage the SSM documents I've already created in order to build an image rather than using another provisioner such as the shell provisioner.

#### Potential configuration

```
{
...,
"provisioners": [
{
"type": "ssm",
"docs": [
{
"name": "myfancyssmdoc",
"parameters": {
"input1": "foo",
"input2": "bar"
}
},
{
"name": "anothercooldoc"
}
]
}
]
}
```

#### Potential References

https://docs.aws.amazon.com/systems-manager/latest/userguide/documents.html