Add SSM resolver

[ocrawford555]

AWS SSM can store values of parameters which end up getting used in CloudFormation templates. We currently have no support of these values in the templates and cannot perform accurate analysis when used.

This PR should be able to handle cases of {{resolve:ssm:parameter-name:version}}.

def test_resolve_ssm():
    template = {
        "AWSTemplateFormatVersion": "2010-09-09",
        "Description": "Test resolving SSM dynamic values",
        "Resources": {
            "InstanceHTTPTargets": {
                "Type": "Custom::DynamicNLBTarget",
                "Properties": {
                    "ServiceArn": "{{resolve:ssm:some-service-arn:1}}",
                    "Cluster": "{{resolve:ssm:main-k8s-cluster-arn:3}}",
                },
            }
        },
    }
    model = parse(template).resolve(extra_params={"some-service-arn:1": "vpc-123-abc"})
    assert model.Resources["InstanceHTTPTargets"].Properties == {
        "Cluster": "UNDEFINED_PARAM_main-k8s-cluster-arn:3",
        "ServiceArn": "vpc-123-abc",
    }

[ignaciobolonio]

LGTM