Improve error message for bulk export in FHIR batches & transactions

[CaitlinV39]

User story
Currently, export requests in batches and transactions will return a 400 because the Accept and Prefer headers cannot be provided. The error message specifies: "Value supplied for the "Accept" header is not supported.".

Instead, return Not Supported and update the error message to explain that export operations are not supported in batches and transactions.

Acceptance criteria
If users try to put an export request in a batch or transaction, it will fail with an appropriate error message.

[mattkoch614]

Hi @CaitlinV39 - Can you provide an example of a request URI a user would make that results in this 400?

Are you referring to export as defined here: http://hl7.org/fhir/us/bulkdata/2019May/export/index.html ?

[CaitlinV39]

@mattkoch614 Yes, that is the export we are looking at. Basically on this you can't invoke $export from within a bundle. This item is tracking to update the error message to make it a little clearer that you are doing an unsupported method.