`offer plan create` - returns invalid json properties

[kevinhillinger]

1. The response from create command is return invalid JSON property names, using snake case instead of camelcase
2. There are properties that shouldn't be returned including the internal id and type of "AzureSkuVariant" since these can remain internal

Example

{
  "certificationsAzureGovernment": [],
  "cloud_availabilities": [
    "public-azure"
  ],
  "conversion_paths": "*",
  "extended_properties": [],
  "external_id": "kehillitestplan2",
  "friendly_name": "test plan 2",
  "id": "bd3ef55d-1558-4929-94a3-99e28d9cbb4d",
  "odata_etag": "\"0315a352-0000-0800-0000-63bef01d0000\"",
  "resource_type": "AzureSkuVariant",
  "state": "Active"
}