Logging response body in APICast Logging Policy

Currently APIcast cannot log the response body using the Logging Policy, as the liquid reference to the response body is not available.

Our recommendation is typically to integrate with Fuse to perform this action, but this requirement can be seen as burdensome for this use case.

This RFE is to expose the response body env var in some fashion so that it can be included in the liquid of the logging policy.