Send only basic checkpoint info on creation

What does this MR do and why?

When a checkpoint is created, we currently send back all the related information (checkpoint, checkpoint writes). This information can be up to 4mb, but it's not used.

On Workhorse side we limit the response body to 1mb and since the body is truncated, Duo Workflow Service receives an invalid json (logs).

We can consider extending the limit (at least to be able to serve GETs), but if this information is not used, maybe we can avoid sending this info for POSTs to reduce some workload.