(aws role) the default description on a role should be None instead of ""

[Steven Moy]

Describe the bug
Current implementation of IAM role default is "". I notice AWS IAM role can have no description. For example, an IAM role results from AWS CLI get-role is the following

{
    "Role": {
        "Path": "/aws-reserved/sso.amazonaws.com/",
        "RoleName": "REDACTED",
        "RoleId": "REDACTED",
        "Arn": "arn:aws:iam::REDACTED:role/aws-reserved/sso.amazonaws.com/REDACTED",
        "CreateDate": "2023-01-03T20:17:20+00:00",
        "AssumeRolePolicyDocument": {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Principal": {
                        "Federated": "arn:aws:iam::REDACTED:saml-provider/AWSSSO_REDACTED_DO_NOT_DELETE"
                    },
                    "Action": [
                        "sts:AssumeRoleWithSAML",
                        "sts:TagSession"
                    ],
                    "Condition": {
                        "StringEquals": {
                            "SAML:aud": "https://signin.aws.amazon.com/saml"
                        }
                    }
                }
            ]
        },
        "MaxSessionDuration": 43200,
        "RoleLastUsed": {
            "LastUsedDate": "2023-04-25T23:18:58+00:00",
            "Region": "us-east-1"
        }
    }
}

That would mean if a user manually run import and submits a pull request. IAMBIC plan would claim the request will attempt to change the cloud because cloud have a description of None. and template simply use "".

To Reproduce
Steps to reproduce the behavior:

1. One sanity is if run import on IAM role with no description.
2. examine resulting yaml file to see if description appeared. (it should not be)
3. run iambic plan. the expectation is there is no changes requires.
4. The bug is it attempt to change to description with empty string.

Expected behavior
Expectation is import, plan should yield no change (as long as there is change in the cloud resource)

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