fhir-eswatini: errors come back with escaped JSON

[josephjclark]

When the fhir server returns an error from http.post, the response body has string encoded JSON.

I've truncated a response but it looks a bit like this:

{
  "body": "{\"resourceType\":\"OperationOutcome\",\"issue\":[{\"ext
  "duration": 695,
  "headers": {
    "connection": "keep-alive",
    "content-length": "22088",
    "content-type": "application/fhir+json; charset=utf-8",
    "date": "Fri, 20 Mar 2026 16:06:11 GMT",
    "keep-alive": "timeout=5",
    "vary": "Accept-Encoding",
    "x-openhim-transactionid": "69bd707380863bf16a1b4ff8"
  },
  "message": "POST to http://172.209.216.154:5001/fhir returned 422: Unprocessable Entity",
  "method": "POST",
  "statusCode": 422,
  "statusMessage": "Unprocessable Entity",
  "url": "http://172.209.216.154:5001/fhir"
}