[WIP] Add Deployments API support

## Add support for deployments API

This pull request includes the following functions:
- Support for preview APIs at the client level
- List/Create Deployments
- List/Create Deployment Statuses
because a maps zero value is nil, this doesn't need to be a pointer.

Do we know for sure that payload will also be a JSON object?  The fact that it's a string on input and object on output makes me nervous.  If this field is polymorphic, then this is likely going to need to be a `json.RawMessage`.  Maybe try throwing different values into the API and see if they all come back as objects?