feat(automation_tokens): Add support for automation-tokens

[Jesse-Hills]

This PR aims to add support for Automation Tokens, as requested in #474.

There are a few things worth mentioning about this implementation, mostly due to the Automation Tokens docs being inaccurate.

• DELETE doesn't work for the /automation-tokens endpoint. The examples don't work as documented, and inspecting requests in the web UI using developer tools shows the web UI using the /tokens endpoint, even for automation tokens. (it appears to be an issue with the endpoint expecting a customer_id in the request, but there is no documentation on it being required or how to pass it in the request)
• The request/response data is inconsistent with the documentation and what is actually expected/returned from the API, some appear to return some form of JSON:API, while others return regular JSON.
• /automation-tokens/{id}/services is supposed to return a list of services associated with the provided token id, also doesn't appear to work, so I haven't included it in this PR, but the same can be achieved using GetAutomationToken and accessing the Services field of the returned AutomationToken.

[kpfleming]

This is not a review yet (although I'll assign myself), but all of those documentation problems should be addressed in the api-documentation repository, because they mean that our generated API clients are also broken since they are generated from those documented schemas.

[kpfleming]

Just some minor doc comments.