HTTP return preference support

[andy-a-o]

Is your feature request related to a problem? Please describe.
https://www.hl7.org/fhir/STU3/http.html#2.21.0.5.2

These interactions are performed using POST, PUT or PATCH, and it may be appropriate for a server to return either only a status code, or also return the entire resource that is the outcome of the create or update (which may be different to that provided by the client). In the case of transactions this means returning a Bundle with just the Bundle.entry.response populated for each entry, and not the Bundle.entry.resource values.

The client can indicate whether the entire resource is returned using the HTTP return preference :

Prefer: return=minimal
Prefer: return=representation
Prefer: return=OperationOutcome

Describe the solution you'd like
Prefer header support implemented as in the spec.

Failed tests
TransactionAndBatchTest (XFER5)