Include email API error responses in HTTP response (#19)

# Description
Include response error messages in email error responses

# Issues
Response messages updated in
NeonGeckoCom/neon_email_proxy#28

# Other Notes
<!-- Note any breaking changes, WIP changes, requests for input, etc.
here -->

Co-authored-by: Daniel McKnight <[email protected]>

neon_hana/mq_service_api.py

@@ -119,7 +119,8 @@ def send_email(self, recipient: str, subject: str, body: str,
         response = send_mq_request("/neon_emails", request_data,
                                    "neon_emails_input")
         if not response.get("success"):
-            raise APIError(status_code=500, detail="Email failed to send")
+            error = response.get("error") or "Email failed to send"
+            raise APIError(status_code=500, detail=error)
 
     def upload_metric(self, metric_name: str, timestamp: str,
                       metric_data: Dict[str, Any]):