fix(IBM): correctly extract secret data for IBM IAM credentials type secrets

[mailtokun]

The result of IAM credentials type is difference from other types. It does not contains a secret_data field.
Below is an example:

{
  "metadata": {
    "collection_type": "application/vnd.ibm.secrets-manager.secret+json",
    "collection_total": 1
  },
  "resources": [
    {
      "access_groups": [
        "AccessGroupId-xxxxx"
      ],
      "api_key": "xxxxxx",
      "created_by": "xxx-xxxxx",
      "creation_date": "2021-07-12T04:57:49Z",
      "crn": "crn:v1:bluemix:public:secrets-manager:us-east:a/xxxx:xxxxx:secret:xxxxx",
      "id": "xxxxx",
      "labels": [
        
      ],
      "last_update_date": "2021-07-12T05:58:27Z",
      "name": "to-be-delete",
      "reuse_api_key": false,
      "secret_type": "iam_credentials",
      "service_id": "ServiceId-xxxxxx",
      "state": 1,
      "state_description": "Active",
      "ttl": 86400
    }
  ]
}

[mailtokun]

@Flydiverny @silasbw Could you review this PR? Thanks.

[Flydiverny]

PR seems accurate, tried checking API docs to confirm https://cloud.ibm.com/apidocs/secrets-manager#get-secret 😄